GH-116738: document thread-safety of bisect

[nascheme]

I don't think it makes sense to make these functions thread-safe. They are already unsafe when used in the default build. And, given that they can operate on any sequence object, trying to lock the sequence object doesn't make sense.

I added a unit test because I believe these functions should not crash or produce TSAN warnings when they are used on a sequence being mutated in another thread.

• Issue: Audit all built-in modules for thread safety #116738

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📚 Documentation preview 📚: https://cpython-previews--136555.org.readthedocs.build/

[picnixz]

Possible suggestions:

• Use a .. note:: if you think users should know about it.
• Use a .. warning:: if you think users should be careful about it.
• Do not use either of them if you think it's just good that users know about it (a note or a warning is quite visible in the sense that it creates a box where the entire content is inside that box).
• Use a subsection about thread-safetiness. Or use a small warning box just saying that the functions are not thread-safe, and add a link to a section at the bottom of the page that contains more detailed explanations.

cc @hugovk

[picnixz]

Suggested change

	.. note::
	The functions in this module are not thread-safe. If multiple threads
	concurrently use :mod:`bisect` functions on the same sequence, this
	may result in undefined behaviour. Likewise, if the provided sequence
	is mutated by a different thread while a :mod:`bisect` function
	is operating on it, the result is undefined. For example, using
	:py:func:`~bisect.insort_left` on the same list from multiple threads
	may result in the list becoming unsorted.
	.. note::
	The functions in this module are not thread-safe. If multiple threads
	concurrently use :mod:`bisect` functions on the same sequence, this
	may result in undefined behaviour. Likewise, if the provided sequence
	is mutated by a different thread while a :mod:`bisect` function
	is operating on it, the result is undefined. For example, using
	:py:func:`~bisect.insort_left` on the same list from multiple threads
	may result in the list becoming unsorted.