asyncio: compute the event loop's clock resolution once, in asyncio.constants #161032

Each BaseEventLoop.__init__ calls time.get_clock_info('monotonic').resolution and stores the result in the private attribute self._clock_resolution, which only _run_once reads. The clock resolution belongs to the platform and process, not to a loop, and it never changes at runtime.

I propose computing it once as asyncio.constants.CLOCK_RESOLUTION, next to the other asyncio tuning values. _clock_resolution is private and undocumented, so the public API doesn't change.

Linked PRs

• gh-161032: Convert BaseEventLoop._clock_resolution to asyncio.constants.CLOCK_RESOLUTION #161033