Add ruff formatting and safe fixing, pyproject-fmt, clean up root

[bollwyvl]

References

• fixes #152
• includes #148

Changes

• [x] add pyproject-fmt
• [x] replace black and isort with ruff
• [x] enable a lot of the rules (mostly cribbed from doitoml)
• [x] apply ruff to
  • [x] .py files
  • [x] .ipynb files
• [x] treat all pytest warnings as errors
  • [x] grandfather in asyncio.get_loop because :shrug:
• [x] ensure cli test files made in tmp_path
• [x] move generated .* files to build
  • [x] .pytest_cache
  • [x] .ruff_cache
  • [x] .coverage
• [x] fix CI step summary
  • example
  • https://github.com/deathbeds/importnb/actions/runs/6755880799?pr=153#summary-18364762697
  • 

[bollwyvl]

No further changes planned, have some more thoughts on #154