Create new ASYNC3xx rules to account for asyncio's different cancellation semantics?

[Zac-HD]

In #211, we noted that ASYNC102 (await-in-finally-or-cancelled) is specific to Trio/AnyIO style "level-triggered" cancellation semantics.

Asyncio has a pretty different system, where cancellation is an event rather than a state (well, mostly - on Python 3.11+ there's also Task.uncancel() to reverse the state change, on 3.10 and earlier you can only partly uncancel).

If someone works out a good lint rule, or set of rules, for asyncio-style cancellation semantics, we'd be happy to accept them as ASYNC3xx rules and make ASYNC102 specific to Trio and AnyIO.