quattro.fail_after(0) and and quattro.fail_after(-1) cancellation is delayed

[graingert]

see also python/cpython#95051

Bug report

I expect this to raise a TimeoutError:

async def amain():
    with quattro.fail_after(-11):
        await asyncio.sleep(0)

asyncio.run(amain())

Instead I have to add an extra asyncio.sleep(0) to get a TimeoutError

async def amain():
    with quattro.fail_after(-11):
        await asyncio.sleep(0)  # does not raise CancelledError
        await asyncio.sleep(0)  # raises CancelledError

asyncio.run(amain())

Your environment

• CPython versions tested on: 3.10 and 3.11
• Operating system and architecture:

here's a comparison, note that uvloop's call_later behaves like call_soon in this case:
https://gist.github.com/graingert/7628f87a629d15cce88f91d6c8cbb1b6

[Tinche]

This got fixed!