chore: replace flake8, flake8-spellcheck, isort and black with ruff and codespell #811
Description
Replace flake8, flake8-spellcheck, isort and black with ruff and codespell. Motivation: ruff is insanely fast. For the conversion, it won't be possible to maintain both systems side-by-side, as there are known deviations from black.
This will touch a few source files, but shouldn't be too drastic (like #137).
- ruff normalizes hex to lower case (black doesn't).
- ruff forces an additional newline following a module docstring.