Use stop-the-world to make `sys._current_frames()` and `sys._current_exceptions()` thread-safe in free-threaded build

[colesbury]

Feature or enhancement

The sys._current_frames and sys._current_exceptions functions rely on the GIL for thread-safety. We should use the stop the world mechanism to pause other threads so that we can safely capture the current frames and exceptions in other threads in the free-threaded build.

Linked PRs

• gh-117300: Use stop the world to make sys._current_frames and sys._current_exceptions thread-safe. #117301