import annotations from __future__ and update annotations

[jakkdl]

Realized this is a thing ... why haven't we used this all along?? Managing typing imports have been a bit of a pain.

Also shed refactors all the annotations, so only manual step was adding the import at the top of the files 💯
(and manually running shed against the .pyi files since new version hasn't been released)

I kinda want one of the checkers we use to suggest importing annotations from future whenever it encounters importing built-ins from typing

[Zac-HD]

Ah, I've habitually avoided from __future__ import annotations because it breaks runtime introspection for (e.g.) Hypothesis, Pydantic, and Typeguard, and at work we're on 3.10 anyway. However runtime introspection is not really a relevant concern for flake8-trio, so let's do it!

(happily PEP-649 will be the real future, so this will work itself out eventually)

[jakkdl]

Ah, I figured there would be some kind of reason it's not used everywhere - makes sense.

ooh, fancy! Looking forward to doing from __future__ import co_annotations instead 😄