gh-140414: add fastpath for current running loop in `asyncio.all_tasks` (#140542)

gh-140414: add fastpath for current running loop in `asyncio.all_tasks` (#140542)

Optimize `asyncio.all_tasks()` for the common case where the event loop is running in the current thread by avoiding stop-the-world pauses and locking.

This optimization is already present for `asyncio.current_task()` so we do the same for `asyncio.all_tasks()`.