Update Python type annotations to modern syntax and types

[scotts]

Fixes #1033.

I did not do this manually. :) Claude did the conversions, with a few rounds of prompting. I had to do some manual un-doing of changes to our tutorials, as those are formatted for the particular rendering we get.

Note that one actual change is that I upped our Python version in pyproject.toml. Because we never bumped that up from 3.8, Claude initially put from __future__ import annotations all over the place.

[NicolasHug]

Thanks, this is much nicer!

I think we'll want a linter rule now, to enforce the new style? pyupgrade looks like what we'd want. It comes with pre-commit hooks too, so we can put it on the CI.

I ran it locally on this PR with:

find src -type f | grep ".py$" | xargs pyupgrade --py310-plus

and the good news is that your PR is spot-on, the only added changes were:

from typing import Generator  # before
from collections.abc import Generator  # now

There were a few more minor changes in the test.

[scotts]

@NicolasHug, yup, agreed, I created #1102 to track the CI change.