Use `PyMutex` in the buffered I/O module

[ByteFlowing1337]

Feature or enhancement

Proposal:

The buffered I/O module currently uses the obsolete PyThread_type_lock. I propose migrating it to the more performant PyMutex.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-154707: Replace PyThread_type_lock with PyMutex in bufferedio.c #154708