gh-125139: use _PyRecursiveMutex in _thread.RLock

[kumaraditya303]

• Issue: _thread.RLock.release is not safe in free-threaded builds #125139

[kumaraditya303]

Current status:

• Windows failed to build on CI but passed locally.
• WASI failure, no idea
• Thread sanitizer failed on CI but passes locally.

[colesbury]

Oh, my hypothesis for the WASI failure is:

• PyThread_get_thread_ident_ex() is zero on WASI
• So an unlocked recursive mutex looks like it's owned by the current thread