gh-116720: Fix corner cases of taskgroups by gvanrossum · Pull Request #117407 · python/cpython

This fixes the one failing test in test_timeouts.
Surprisingly, it doesn't break any other asyncio tests.

Also switch to consistently using internal/external
instead of inside/outside.

This prevents external cancellations of a task group's parent task to
be dropped when an internal cancellation happens at the same time.
Also strengthen the semantics of uncancel() to clear self._must_cancel
when the cancellation count reaches zero.

Co-Authored-By: Tin Tvrtković <tinchester@gmail.com>
Co-Authored-By: Arthur Tacca