Problems with lingering threads during/after runtime finalization continue to be a problem.  I'm going to use this issue as the focal point for efforts to resolve this.


Related issues:
* #36479 "Exit threads when interpreter is finalizing rather than runtime."
* #24770 "Py_Finalize() doesn't stop daemon threads"
* #23592 "SIGSEGV on interpreter shutdown, with daemon threads running wild"
* #37127 "Handling pending calls during runtime finalization may cause problems."
* #33608 "Add a cross-interpreter-safe mechanism to indicate that an object may be destroyed."
* #36818 "Add PyInterpreterState.runtime."
* #36724 "Clear _PyRuntime at exit"
* #14073 "allow per-thread atexit()"
* #1596321 "KeyError at exit after 'import threading' in other thread"
* #37266 "Daemon threads must be forbidden in subinterpreters"
* #31517 "MainThread association logic is fragile"