#15290: Fix UAF issue with Singleton destruction order (#15689)

### Ticket
[Link to Github
Issue](#15290)

### Problem description
There are a number of Singletons being used in tt-metal: `SystemMesh`,
`DevicePool`, `Cluster`. There's a corner case that popped up that
caused a UAF error where `SystemMesh` was already destructed before
MeshDevice.

### What's changed
- Decouple MeshDevice destruction from SystemMesh destruction.
- Refactor SystemMesh to encapsulate internals in pImpl class.
- Added a new test case for SystemMesh tear down with static mesh in the
distributed tests.

### Checklist
- [x] Post commit CI passes
- [ ] Blackhole Post commit (if applicable)
- [x] Model regression CI testing passes (if applicable)
- [ ] Device performance regression CI testing passes (if applicable)
- [x] New/Existing tests provide coverage for changes

https://github.com/tenstorrent/tt-metal/actions/runs/12198356189
https://github.com/tenstorrent/tt-metal/actions/runs/12194392381

tests/ttnn/distributed/CMakeLists.txt

@@ -1,4 +1,8 @@
-add_executable(test_distributed test_distributed.cpp)
+add_executable(
+    test_distributed
+    test_distributed.cpp
+    test_distributed_atexit.cpp
+)
 
 # Set up properties for the target
 setup_ttnn_test_target(test_distributed)

tests/ttnn/distributed/test_distributed_atexit.cpp

@@ -0,0 +1,26 @@
+// SPDX-FileCopyrightText: © 2024 Tenstorrent Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+#include <gtest/gtest.h>
+
+#include <cstddef>
+#include <ttnn/core.hpp>
+#include <ttnn/distributed/api.hpp>
+#include "distributed/mesh_device.hpp"
+
+namespace ttnn::distributed::test {
+
+// Simplified test without fixture, and mesh variable moved inside test
+TEST(DistributedTestStandalone, TestSystemMeshTearDownWithoutClose) {
+    static std::shared_ptr<ttnn::MeshDevice> mesh;
+    auto& sys = tt::tt_metal::distributed::SystemMesh::instance();
+    mesh = ttnn::distributed::open_mesh_device(
+        {2, 4}, DEFAULT_L1_SMALL_SIZE, DEFAULT_TRACE_REGION_SIZE, 1, tt::tt_metal::DispatchCoreType::WORKER);
+
+    auto [rows, cols] = sys.get_shape();
+    EXPECT_GT(rows, 0);
+    EXPECT_GT(cols, 0);
+}
+
+}  // namespace ttnn::distributed::test