Add Ruff formatting & linting

[NiklasRosenstein]

This PR adds Ruff as a development dependency and uses it in CI to check for lints and to enforce formatting.

[NiklasRosenstein]

Seems you gave me permissions to merge without waiting for your review, @marzzzello. I'll wait anyway to be sure. 🙂

Side note, I've just changed the settings to disable merge commits and rebase merging and leave only squash merging. It results in a much leaner commit history. Lmk if you dislike that

[RealCLanger]

Cool, I think this looks so much nicer than using "black".

However, in the readme, we have a reference to black:
https://github.com/pytr-org/pytr?tab=readme-ov-file#linting-and-code-formatting

Can you mention ruff there and, if it conflicts (which I believe it does), maybe drop black there?

[NiklasRosenstein]

Indeed, thanks for the notice. I've updated the README now