Add from __future__ import annotations using Ruff/isort

[hugovk]

Helps #2625.

Adds the from __future__ import annotations to all files, and will ensure it's added for new files too, so we can use newer type annotations for older Pythons.

For example, use list and tuple directly instead of first from typing import List, Tuple.

[radarhere]

I see you've added it to the test suite as well. I would have thought that the goal of #2625 was to add type hints to user-facing code. Or are you suggesting that expecting that we will eventually use type hints for their own sake?

[hugovk]

User-facing code is the primary focus, but typing tests can also be beneficial, especially if it helps evaluate how the typed production code is used, and if it helps us find bugs in tests.

See also https://sethmlarson.dev/tests-arent-enough-case-study-after-adding-types-to-urllib3#type-your-tests