Enforce modern best practices concerning annotations, typing and symbol import/export

[Avasam]

Overlaps with #101, probably merge that one first to reduce changes.

Mostly taken from my own shared config file: https://github.com/Beslogic/Beslogic-Ruff-Config/blob/main/ruff.toml
But scoped to only rule groups that concern modernization and best practices for annotations, typing and symbol import/export.
Most of this was autofixed.

The most immediate effects here are:

• Reduced imports (which will keep reducing in time and as older Python versions are dropped)
• Reduced static typing workarounds
• Avoid evaluating typing symbols when unnecessary
• Return type annotations on public functions (mypy will infer Any if return type annotation is missing, where every other type checker will infer from the function body)
• Explicit re-exports so that type-checkers don't have to guess if the symbols are meant to be public or internal
• More correctness checks
• General alignments with the rest of the Python Typing ecosystem

[Avasam]

E722 done in #103
It's a base Ruff rule, so felt out of scope for this PR.

[Kalmat]

Sorry. Should I merge this PR or just wait?

[Avasam]

#101 has been merged. You can merge this now.

I tried to keep my PRs as isolated as possible for review and history. Of course I expected some overlap and conflicts.