Move from flake8 to Ruff

[TeaDrinkingProgrammer]

When #1973 is merged, it makes sense to also move from Flake8 to Ruff. Ruff is a tool from the same company (astral) and has similar appeal to UV:

• Very fast
• Combines multiple tools (Flake8, isort and Black)
• Pyproject.toml support (Flake8 is not adding this soon)
• Nice warnings/errors
• Good editor integration

Ruff have a FAQ item dedicated to comparing Flake8 with Ruff.

Also see the following experiences from people migrating to Ruff:

• https://daftdev.blog/2024/03/25/migrating-to-ruff-from-black-and-flake8/

This tool can be used to make a start:

• https://pypi.org/project/flake8-to-ruff/

I don't mind making a start, but of course, I don't know which rules you want to apply, which you don't and whether or not you want to add new rules.