Embrace the __future__ of typing

[ivirshup]

This PR moves the codebase towards using more contemporary typing patterns via the from __future__ import annotations backport mechanism. Main changes are:

• dict[str, str], list[int] instead of from typing import Dict, List, Dict[str, str], List[int]
• int | str instead of from typing import Union Union[int, str]
• int | None instead of Optional[int]

Turns out this needed a little bit of manual work. For now, here is a demo of what this looks like. I've covered the main census API, but not the tests or experimental yet.

[ivirshup]

I need to look into the failure, iirc this may be fixable with typing-extensions