gh-145254: Add thread safety annotation

[lysnikolaou]

• Implement annotation for different thread safety levels
• Annotate PyMutex_* APIs

• Issue: Add thread safety annotations for C API functions #145254

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📚 Documentation preview 📚: https://cpython-previews--145255.org.readthedocs.build/en/145255/c-api/synchronization.html#c.PyMutex_Lock

[hugovk]

python/python-docs-theme#297 is merged and released in https://github.com/python/python-docs-theme/releases/tag/2026.2

Fix the lint with uvx prek run --all-files or uvx prek run --all-files ruff-format.

And as a bonus, the docs will rebuild with the new theme.

[hugovk]

Will this be backported?

Even if so, perhaps use frozendict on main?

Suggested change

	_THREADSAFETY_DISPLAY = {
	"incompatible": "Not safe to call from multiple threads.",
	"compatible": "Safe to call from multiple threads with external synchronization only.",
	"safe": "Safe for concurrent use.",
	}
	# Maps each thread safety level to the glossary term it should link to.
	_THREADSAFETY_TERM = {
	"incompatible": "thread-incompatible",
	"compatible": "thread-compatible",
	"safe": "thread-safe",
	}
	_THREADSAFETY_DISPLAY = frozendict(
	incompatible = "Not safe to call from multiple threads.",
	compatible = "Safe to call from multiple threads with external synchronization only.",
	safe = "Safe for concurrent use.",
	)
	# Maps each thread safety level to the glossary term it should link to.
	_THREADSAFETY_TERM = frozendict(
	incompatible = "thread-incompatible",
	compatible = "thread-compatible",
	safe = "thread-safe",
	)