ASYNC102 no longer raises warning for calls to `.aclose()` on objects

[jakkdl]

See #156

I'm not sure if #156 also covers more general discussion on if/how to overhaul async102 and should remain open after this is merged.

[Zac-HD]

Very quick notes:

• we should allow this in an except clause too
• only exempt if the call takes no arguments, i.e. still error on await x.aclose(foo)
• don't exempt asyncio-only code; this is a trio/anyio semantics thing
• merge conflict from the other PR 😅

and then I think we're ready and it'll close the linked issue.

[jakkdl]

don't exempt asyncio-only code; this is a trio/anyio semantics thing

I interpreted this as "if running with --anyio and not importing anyio/trio, or only importing asyncio => don't mark as safe; but if running with --anyio and/or importing anyio/trio and importing asyncio => mark as safe", so if you have a mixed project it'll lean towards not reporting acloses. But I could make it more aggressive and warn if there's any risk that this part concerns asyncio-code (i.e. asyncio in self.library -> "running with --asyncio; or asyncio is imported")