Add builds for modern python versions

[jonbannister]

We should build at least: 3.8, 3.10, 3.11, 3.12 and aim for 3.13.

[offbyone]

Do you want PRs for this? I'm about to spend some time on a plane, and that's prime "mess around with CI" time :D

[jonbannister]

I mean - sure, why not! This is how far I got a few weeks ago master...add-new-py-versions

[offbyone]

How wedded to the current setuptools workflow are you? Are you okay with changing up the dev environment, or is there a standard interaction you want to preserve?

I ask because lately I've been switching all my packages over to uv and lemme tell you... it is nice.

[jonbannister]

Feel free to try - I suspect there may be some custom setuptools hooks that you would need to replace. As long as the build artefacts are the same I don't mind either way :)