GeezerVison

This PR introduces a dedicated regression test to Lib/test/test_threading.py to prevent future namespace collisions on the _handle attribute within the threading.Thread class lifecycle.

Rationale

In Python 3.13, the introduction of an internal _handle tracking parameter inadvertently shadowed custom _handle methods or attributes defined by third-party frameworks (such as gevent) which subclass threading.Thread. While the core engine has since migrated its internal variable to _os_thread_handle to resolve the conflict, an explicit test suite assertion was missing. This regression test ensures that user-defined subclasses can natively implement a custom self._handle attribute without interfering with standard library operations or causing unexpected runtime behavior.

Verification

• Ran the local test suite on the modified source tree: ./python -m test test_threading -v
• Verified that all 246 tests completed successfully with zero regressions or errors.

• Issue: Introduction of Thread._handle: _thread._ThreadHandle in Python3.13 has broken an unknown number of packages #132578