Make `_threadmodule.c` thread-safe in `--disable-gil` builds

[mpage]

Feature or enhancement

Proposal:

Make the functionality in _threadmodule.c thread-safe in free-threaded builds.

Commits from nogil-3.12: https://github.com/colesbury/nogil-3.12/commits/nogil-3.12/Modules/_threadmodule.c

Context from @colesbury:

• Ignore the CriticalLock commit; this was an idea that didn't work and was prone to deadlock.
• Ignore the weakrefs change.
• Unclear if we need to deal with _tstate_lock.
• For the other changes, use your judgement. You may be able to put together smaller changes
• _Py_ThreadId() is currently only available in the free-threaded build, so the recursive lock implementation can probably (?) just stick with the existing PyThread_get_thread_ident().

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-114271: Fix race in Thread.join() #114839
• gh-114271: Make PyInterpreterState.threads.count thread-safe in free-threaded builds #115093
• gh-114271: Make thread._rlock thread-safe in free-threaded builds #115102
• gh-114271: Make _thread.ThreadHandle thread-safe in free-threaded builds #115190
• gh-114271: Make _thread.lock thread-safe in free-threaded builds #116433
• gh-114271: Clean Up _threadmodule.c #116776

[mpage]

@colesbury - Would you assign this to me, please?