chore: use annotations from the __future__

[tonyandrewmeyer]

The goal here is to reduce the use of the name "Scenario" in the docs, to control where it appears when the docs are included at ops.readthedocs.io.

Using from __future__ import annotations seems to make Sphinx much happier when doing the class signatures, avoiding odd text like ~scenario.state.CloudCredential instead of the expected link with text "CloudCredential" and destination that class.

When adding those imports, pyupgrade transformed all the type annotations - I wasn't previously aware that the future import made this possible in 3.8, but it seems to be the case. I've run all the tests with 3.8, 3.9, 3.10, 3.11, and 3.12 and they all pass, and I've manually tested in 3.8 and everything seems to work without any problems. I like this much more, so it seems like a win-win.

The pyupgrade pre-commit hook seemed to be running twice, so I've removed the duplication, and bumped the version from 3.7 to 3.8, and removed what looks like an out-of-date exclusion. I've also changed pyright to target 3.8 compatibility.

A couple of docstrings are changed to use the State() style rather than scenario.State() style.

[tonyandrewmeyer]

Huh, but then it fails in CI. Weird. I'll move to draft and look into this more later.