Add Ruff linter and formatter.

[S-aiueo32]

Thanks for a great repository.

I am currently trying to read through your repository and was concerned about the lack of uniformity in formatting, which reduces readability.

This PR introduces Ruff, a modern linter/formatter, and applies mechanical fixes to the code with the following commands:

$ poetry run ruff check . --fix
$ poetry run ruff format .

[neonwatty]

Very easy add and would standardize things nicely.