Replace isort and black with ruff

[ItsDrike]

Recently (a while ago to be fair, but this project wasn't really updated for a long time), ruff has introduced their own formatter, which aims to replace black. It is almost 1:1 compatible with black, as can be seen by the small amount of changes made to the existing code.

Additionally, this also replaces isort with the built-in isort support in ruff. This was a feature for quite a while now, but there were some incompatibilities with isort, as not all isort settings were previously supported. That has since changed, and ruff now supports isort in the same configuration that we were using before.This therefore allows us to get rid of isort too.

This is a good thing, as it shouldn't introduce any real differences to the code style, while reducing the amount of necessary tools that contributors need to be working with, and even improving speed, as ruff is faster than isort or black (although realistically, pre-commit still won't be super fast, as pyright is the significant slow-down there).

Furthermore, this PR also updates ruff lint settings in pyproject.toml, adding some extra rules, and more importantly, renaming now deprecated section names for configuring ruff lint (ruff.* was changed to ruff.lint.*).

Task List:

• Update the version of ruff that's being used to latest, and fix any new violations as a result of this update
• Drop isort in favor of ruff's isort lint module
• Drop black in favor of ruff formatter
• Update pre-commit to use ruff instead of black & isort
• Update GitHub workflows to use ruff instead of black & isort
• Update contributing documents that mention black & isort in favor of ruff (this also adds an entry on slotscheck tool, which wasn't previously documented at all for some reason)