add: C APIの`#[repr(Rust)]`なものへのアクセスをすべて安全にする #2969

Job	Run time
actionlint	19s
rust-lint	3m 40s
shellcheck	12s
validate-cargo-lock	23s
build-and-test-java-api (windows-latest)	6m 4s
build-and-test-java-api (macos-latest)	3m 12s
build-and-test-java-api (ubuntu-latest)	2m 57s
build-and-test-python-api (windows-latest)	7m 22s
build-and-test-python-api (macos-latest)	3m 33s
build-and-test-python-api (ubuntu-latest)	3m 3s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	1m 34s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	1m 40s
build-windows-cpp-example	4m 13s
c-header	47s
rust-integration-test-strategy-matrix	1s
rust-unit-test	5m 18s
rust-integration-test (macos-12)	4m 39s
rust-integration-test (ubuntu-20.04)	2m 19s
	51m 16s

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