Update lower bound python support to 3.10

[chrishalcrow]

Neo 0.14.3 only supports python >= 3.10 (https://github.com/NeuralEnsemble/python-neo/blob/master/pyproject.toml), so we actually already haven't supported 3.9 for a while! All tests etc already use 3.10 as the lower bound.

This PR will make uv stop complaining ;)

Also tried to remove from __futures__ import annotations, Union and Optional. Turns out you need futures for:

• self reference typing in classes. E.g. BaseExtractor.get_parents returns BaseExtractor
• Stuff like method: "std" | None = None. In the future, we'll deal with this properly using Literals. For now, let's use __futures__

[alejoe91]

With 3.10, we can remove all from __future__ import annotations! Can you try to remove them all as part of the PR?

[chrishalcrow]

Was looking at what else we can clean - don't need Union or Optional anymore either!