…mart_holder (test fails)

…stance() specialization. Also bring in dynamic_raw_ptr_cast_if_possible.h. Does not build because try_initialization_using_shared_from_this() is still missing.

…holder_type_casters.h. With this test_wip builds and succeeds.

skip-checks: true

… errors.

…ch (does not build).

…o; harmless).

…with is_same<Holder<Class>, smart_holder> (still does not build).

…() from smart_holder_type_casters.h (with this test_wip builds and runs successfully).

…l (4) BAKEIN_BREAK from test_factory_constructors.py (test_factory_constructors builds and runs successfully).

…st_class).

…ly_holder_caster<unique_ptr>. No functional changes.

…_ptr_to_python() there, add smart_holder_from_unique_ptr()

…ipped tests pass locally with C++17).

…est_files.py

…anymore).

…(replaces BAKEIN_BREAK).

…ranch as-is.

…st.cpp

…d behavior sooner rather than later).

…ny production code changes).

…ult().

…-is (does not build).

…asic.cpp, 26 BAKEIN_BREAK in test_class_sh_basic.py

```
========================================================= short test summary info ==========================================================
SKIPPED [1] test_class_sh_basic.py:59: got empty parameter set ('pass_f', 'rtrn_f', 'expected'), function test_load_with_rtrn_f at /usr/local/google/home/rwgk/forked/pybind11/tests/test_class_sh_basic.py:58
SKIPPED [1] test_class_sh_basic.py:70: got empty parameter set ('pass_f', 'rtrn_f', 'regex_expected'), function test_deleter_roundtrip at /usr/local/google/home/rwgk/forked/pybind11/tests/test_class_sh_basic.py:69
SKIPPED [1] test_class_sh_basic.py:99: got empty parameter set ('pass_f', 'rtrn_f', 'expected'), function test_pass_unique_ptr_disowns at /usr/local/google/home/rwgk/forked/pybind11/tests/test_class_sh_basic.py:98
SKIPPED [1] test_class_sh_basic.py:120: got empty parameter set ('pass_f', 'rtrn_f'), function test_cannot_disown_use_count_ne_1 at /usr/local/google/home/rwgk/forked/pybind11/tests/test_class_sh_basic.py:119
SKIPPED [1] test_class_sh_basic.py:145: BAKEIN_BREAK: AttributeError unique_ptr_roundtrip
SKIPPED [1] test_class_sh_basic.py:157: unconditional skip
SKIPPED [1] test_class_sh_basic.py:169: got empty parameter set ('pass_f', 'rtrn_f', 'moved_out', 'moved_in'), function test_unique_ptr_consumer_roundtrip at /usr/local/google/home/rwgk/forked/pybind11/tests/test_class_sh_basic.py:168
SKIPPED [1] test_class_sh_basic.py:210: BAKEIN_BREAK: AttributeError args_unique_ptr
====================================================== 17 passed, 8 skipped in 0.04s =======================================================```

…extra_python_package/test_files.py

…d_ptr()` functionality from smart_holder branch.

…ptr<T const, D>`

Enables removing:
4 BAKEIN_BREAK in test_class_sh_basic.cpp
2 BAKEIN_BREAK in test_class_sh_basic.py

…ptr<T const>`

Resolves one `// BAKEIN_WIP: Better Const2Mutbl`.

…lue_shared_ptr()`, `load_value_smart_holder()` (the latter just throws right now)

…ctional changes.

```
/__w/pybind11/pybind11/include/pybind11/cast.h:918:44: error: std::move of the variable 'v_h' of the trivially-copyable type 'pybind11::detail::value_and_holder' has no effect [performance-move-const-arg,-warnings-as-errors]
            return load_value_smart_holder(std::move(v_h));
                                           ^
/__w/pybind11/pybind11/include/pybind11/cast.h:911:53: note: consider changing the 1st parameter of 'load_value_smart_holder' from 'pybind11::detail::value_and_holder &&' to 'const pybind11::detail::value_and_holder &'
    bool load_value_smart_holder(value_and_holder &&v_h) {
                                                    ^
/__w/pybind11/pybind11/include/pybind11/cast.h:920:38: error: std::move of the variable 'v_h' of the trivially-copyable type 'pybind11::detail::value_and_holder' has no effect [performance-move-const-arg,-warnings-as-errors]
        return load_value_shared_ptr(std::move(v_h));
                                     ^
/__w/pybind11/pybind11/include/pybind11/cast.h:895:51: note: consider changing the 1st parameter of 'load_value_shared_ptr' from 'pybind11::detail::value_and_holder &&' to 'const pybind11::detail::value_and_holder &'
    bool load_value_shared_ptr(value_and_holder &&v_h) {
                                                  ^
```

…: pass_shmp, pass_shcp

…`type_caster_base<T>`

CRUDE INTERMEDIATE STATE, just to see if this builds on all platforms.

…ld be useful).

…ut 1 block of 4 BAKEIN_BREAK in test_class_sh_basic.py

…ast 3 remaining BAKEIN_BREAK in test_class_sh_basic.cpp

…stead of `return false` (i.e. prefer noisy failure over potentially silent failure).

…se.h. CRUDE intermediate state, needs refactoring.

All 4 remaining BAKEIN_BREAK removed from test_class_sh_basic.py. With that both test_class_sh_basic.cpp and test_class_sh_basic.py are identical to the smart_holder branch.

All unit tests pass ASAN and MSAN testing with the Google-internal toolchain.

…ication.

All unit tests pass ASAN and MSAN testing with the Google-internal toolchain.

…older branch as-is (tests pass without any further changes).

All unit tests pass ASAN and MSAN testing with the Google-internal toolchain.

… that pass without any further changes.

All unit tests pass ASAN and MSAN testing with the Google-internal toolchain.

…older branch as-is (does not build).

All unit tests pass ASAN and MSAN testing with the Google-internal toolchain.

…h as-is (Segmentation fault).

…anch as-is (AssertionError).

….txt

… in type_caster_base.h: the organization of the existing code makes it very difficult to factor the added code properly.

```
========================================================= short test summary info ==========================================================
SKIPPED [4] test_class_sh_disowning_mi.py:67: BAKEIN_BREAK: AssertionError
SKIPPED [2] test_class_sh_disowning_mi.py:43: BAKEIN_BREAK: AssertionError
SKIPPED [2] test_class_sh_disowning_mi.py:54: BAKEIN_BREAK: AssertionError
SKIPPED [1] test_class_sh_basic.py:156: unconditional skip
SKIPPED [6] test_class_sh_mi_thunks.py:34: BAKEIN_BREAK: Segmentation fault
SKIPPED [2] test_class_sh_mi_thunks.py:43: BAKEIN_BREAK: AssertionError
SKIPPED [1] test_class_sh_mi_thunks.py:51: BAKEIN_BREAK: Failed: DID NOT RAISE <class 'ValueError'>
SKIPPED [1] test_stl.py:149: no <experimental/optional>
SKIPPED [1] test_smart_ptr.py:301: BAKEIN_EXPECTED: Failed: DID NOT RAISE <class 'RuntimeError'>
FAILED test_class_sh_basic.py::test_load_with_mtxt[pass_shmp-Shmp-pass_shmp:Shmp(_MvCtor)*_MvCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_b - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_unique_ptr_consumer_roundtrip[pass_valu-rtrn_lref-True-False] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_cannot_disown_use_count_ne_1[pass_udcp-rtrn_udcp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_unique_ptr_roundtrip - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_unique_ptr_consumer_roundtrip[pass_valu-rtrn_cref-True-False] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_load_with_mtxt[pass_uqmp-Uqmp-pass_uqmp:Uqmp(_MvCtor)*_MvCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_load_with_mtxt[pass_uqcp-Uqcp-pass_uqcp:Uqcp(_MvCtor)*_MvCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_load_with_rtrn_f[pass_udmp-rtrn_udmp-pass_udmp:rtrn_udmp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_load_with_rtrn_f[pass_udcp-rtrn_udcp-pass_udcp:rtrn_udcp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_deleter_roundtrip[pass_udcp_del-rtrn_udcp_del-pass_udcp_del:rtrn_udcp_del,udcp_deleter(_MvCtorTo)*_MvCtorTo] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_deleter_roundtrip[pass_udmp_del_nd-rtrn_udmp_del_nd-pass_udmp_del_nd:rtrn_udmp_del_nd,udmp_deleter_nd(_MvCtorTo)*_MvCtorTo] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_deleter_roundtrip[pass_udcp_del_nd-rtrn_udcp_del_nd-pass_udcp_del_nd:rtrn_udcp_del_nd,udcp_deleter_nd(_MvCtorTo)*_MvCtorTo] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning.py::test_same_twice - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning.py::test_mixed - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning.py::test_overloaded - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_pass_unique_ptr_disowns[pass_udmp-rtrn_udmp-pass_udmp:rtrn_udmp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_pass_unique_ptr_disowns[pass_udcp-rtrn_udcp-pass_udcp:rtrn_udcp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_cannot_disown_use_count_ne_1[pass_uqmp-rtrn_uqmp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_cannot_disown_use_count_ne_1[pass_uqcp-rtrn_uqcp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_unique_ptr_consumer_roundtrip[pass_valu-rtrn_valu-True-True] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_pass_unique_ptr_disowns[pass_uqmp-rtrn_uqmp-pass_uqmp:rtrn_uqmp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base1_first[MI1-1-2-None] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_pure_cpp_sft_raw_ptr[make_pure_cpp_sft_unq_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_pure_cpp_sft_raw_ptr[make_pure_cpp_sft_shd_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_basic.py::test_drvd0_add_in_cpp_unique_ptr - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_basic.py::test_drvd1_add_in_cpp_unique_ptr - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_self_life_support.py::test_m_big5 - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_self_life_support.py::test_py_big5[0-Seed_CpCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_virtual_py_cpp_mix.py::test_get_from_cpp_unique_ptr[Base-5101] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_virtual_py_cpp_mix.py::test_get_from_cpp_unique_ptr[PyBase-5323] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2_first[MI1-1-2-None] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2_first[MI2-3-4-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2_first[MI3-5-6-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2_first[MI4-7-8-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_inheritance.py::test_rtrn_shmp_drvd_pass_shcp_base - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_inheritance.py::test_rtrn_shmp_drvd_up_cast_pass_shcp_drvd - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_std_make_shared_factory - AssertionError: assert 'BEAKIN_WIP: ...ype() called.' == 'smart_holder...ed_from_this.'
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_shared_ptr_cpp_arg - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_shared_ptr_cpp_prop - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_shared_ptr_arg_identity - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2[MI6-12-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2[MI7-13-4] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2[MI8-14-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2[MI8b-15-3] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_multiple_registered_instances_for_same_pointee - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_multiple_registered_instances_for_same_pointee_leak - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_virtual_py_cpp_mix.py::test_get_from_cpp_unique_ptr[CppDerivedPlain-5202] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_virtual_py_cpp_mix.py::test_get_from_cpp_unique_ptr[CppDerived-5212] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_stash_leak - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_stash_via_shared_from_this - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_stash_via_shared_from_this_leak - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_pass_released_shared_ptr_as_unique_ptr - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_shared_ptr_goaway - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_infinite - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_std_make_shared_factory[pass_through_shd_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_std_make_shared_factory[pass_through_shd_ptr_release_gil] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_unique_ptr.py::test_m_clone_and_foo - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_unique_ptr_member.py::test_pointee_and_ptr_owner[give_up_ownership_via_unique_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_self_life_support.py::test_py_big5[2-Seed_OpEqLv] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_self_life_support.py::test_py_big5[3-Seed_OpEqRv] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_shared_from_this - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_shared_from_this_leak - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_load_with_mtxt[pass_shcp-Shcp-pass_shcp:Shcp(_MvCtor)*_MvCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base1_first[MI2-3-4-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_unique_ptr_consumer_roundtrip[pass_rref-rtrn_valu-True-True] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base1_first[MI3-5-6-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base1_first[MI4-7-8-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_pass_unique_ptr_disowns[pass_uqcp-rtrn_uqcp-pass_uqcp:rtrn_uqcp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_cannot_disown_use_count_ne_1[pass_udmp-rtrn_udmp] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_unique_ptr.py::test_m_clone - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base2_first[MI5-10-11-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_self_life_support.py::test_py_big5[1-Seed_MvCtor] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_multiple_registered_instances_for_same_pointee_recursive - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_virtual_py_cpp_mix.py::test_get_from_cpp_unique_ptr[PyCppDerived-5434] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_basic.py::test_drvd0_add_in_cpp_shared_ptr - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_release_and_stash - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_basic.py::test_deleter_roundtrip[pass_udmp_del-rtrn_udmp_del-pass_udmp_del:rtrn_udmp_del,udmp_deleter(_MvCtorTo)*_MvCtorTo] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_unique_ptr_member.py::test_pointee_and_ptr_owner[give_up_ownership_via_shared_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_from_this.py::test_pure_cpp_sft_raw_ptr[make_pure_cpp_sft_raw_ptr] - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_trampoline_shared_ptr_cpp_arg.py::test_shared_ptr_alias_nonpython - RuntimeError: BEAKIN_WIP: convert_type() called.
FAILED test_class_sh_disowning_mi.py::test_disown_base1_first[MI5-10-11-1] - RuntimeError: BEAKIN_WIP: convert_type() called.
================================================ 82 failed, 939 passed, 20 skipped in 4.02s ================================================
```

… (tests still fail)

…_raw_ptr-vec_size_base0_shared_ptr]

scons -j 48 selected_test_cpp=test_class_sh_mi_thunks.cpp && "$(cat PYROOT)"/bin/python3 $HOME/clone/pybind11_scons/run_tests.py ../pybind11 test_class_sh_mi_thunks.py -s -vv -k 'test_get_vec_size_raw_shared[get_drvd_as_base0_raw_ptr-vec_size_base0_shared_ptr]'

```
=========================================================== test session starts ============================================================
platform linux -- Python 3.11.8, pytest-7.4.4, pluggy-1.5.0 -- /usr/bin/python3
cachedir: .pytest_cache
C++ Info: 13.2.0 C++20 __pybind11_internals_v10000000_gcc_libstdcpp_cxxabi1018__ PYBIND11_SIMPLE_GIL_MANAGEMENT=False PYBIND11_NUMPY_1_ONLY=False
rootdir: /usr/local/google/home/rwgk/forked/pybind11/tests
configfile: pytest.ini
plugins: xdist-3.5.0
collected 10 items / 9 deselected / 1 selected

test_class_sh_mi_thunks.py::test_get_vec_size_raw_shared[get_drvd_as_base0_raw_ptr-vec_size_base0_shared_ptr]
LOOOK A

LOOOK get raw drvd 47927280

LOOOK get raw base 47927312

LOOOK B

LOOOK shd load(src, convert) X

LOOOK shd try_implicit_casts(src, convert) Q

LOOOK shd try_implicit_casts(src, convert) R

LOOOK shd load(src, convert) X

LOOOK shd load_value(v_h) ENTRY

LOOOK shd load_value(v_h) A

LOOOK shd load_value(v_h) B

LOOOK shd load(src, convert) Y 47927280

LOOOK shd try_implicit_casts(src, convert) S

LOOOK shd load(src, convert) Y 47927312

LOOOK operator std::shared_ptr<type> & A 47927312 /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../cast.h:891

LOOOK /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:838

LOOOK /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:842

LOOOK operator std::shared_ptr<type> & B 47927312 /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../cast.h:893

LOOOK shd const Base0 *obj 47927312

LOOOK shd const auto *obj_der 47927280

LOOOK C
PASSED

===================================================== 1 passed, 9 deselected in 0.01s ======================================================
```

… test_class_sh_mi_thunks tests pass.

…mi.py (tests pass without any further changes).

…y_move.py `test_properties()` (appears to fail on ~17 platforms).

…py_move.py to top level (still appears to fail on ~17 platforms).

… as-is (does not build).

…lder branch as-is (does not build).

… (tests pass without any further changes).

… (tests pass without any further changes).

…on leading to failures in test_class_sh_shared_ptr_copy_move.py:

* Disable all tests in test_class_sh_property_non_owning.py

* Disable only `test_properties()` in test_class_sh_shared_ptr_copy_move.py

* Go back to original .github/workflows/ci.yml

…ss_sh_shared_ptr_copy_move.py (suspected (!) holder mismatch).

…t_class_sh_shared_ptr_copy_move.py

…git clean -fdx

NO SegFault 20.04 C++11 Debug all tests, even in first pass after git clean -fdx
BUT then suddenly SegFaults not reproducible anymore even with MinSizeRel!?

Current thread 0x00007f6c7165e740 (most recent call first):
  File "/mounted_pybind11/tests/test_class_sh_shared_ptr_copy_move.py", line 9 in test_shptr_copy

line 9:
    lst = m.test_ShPtr_copy()

This line was added after last observed SegFault
    del mth

…non_owning.py. Remove pytest.skip() in test_class_sh_shared_ptr_copy_move.py and test_class_sh_property_non_owning.py

…n test_class_sh_disowning.py (pybind#5234)

…tion for debugging behavior difference).

…e_caster_generic::load_value() in shared_ptr and unique_ptr casters.