refactor: adopt ruff as a linter

[AlessandroMiola]

Summary:

• c0179d3:
  • pyproject.toml: add configuration for ruff linter ^{1 2}
  • .pre-commit-config.yaml: add pre-commit hook for ruff (while removing flake8's one) ³
  • .github/workflows/actions.yaml: setup action for ruff linter (while removing flake8's one)
  • leftover: apply ruff and black proposed fixes
• f785b9e:
  • poetry.lock, pyproject.toml, setup.cfg: remove flake8 dependency
  • pyproject.toml: fixable = ["ALL"] is redundant ⁴
  • README.md: update README as a consequence of enforcing the use of ruff over flake8

Footnotes

1. better nest linter-specific configs under [tool.ruff.lint], formatter-specific configs under [tool.ruff.format] and configs common to both linter and formatter under [tool.ruff] (see https://github.com/astral-sh/ruff/discussions/9406) ↩

2. note that

   • ruff's autofix feature is available for most of the lint rules, but not for all of them (eg an autofix for A001 is not available, as I could experience); list of available autofixes at https://docs.astral.sh/ruff/linter/#fix-safety
   • ruff's autofix feature does not apply to unsafe fixes (eg C414, as I could experience); you'd need to promote unsafe fixes to safe by specifying eg extend-safe-fixes = ["C414"] under [tool.ruff.lint] (see https://docs.astral.sh/ruff/linter/#fix-safety) or proceed manually
   ↩

3. be aware of putting ruff's linter hook before any formatter hook (black here) as ruff's --fix might apply changes requiring reformatting, which indeed happened (see https://docs.astral.sh/ruff/integrations/#pre-commit) ↩

4. fixable = ["ALL"] is the default already. Better configure such option in order to specify the (sub)-list of selected (i.e. specified in select =) rules that you would not only check against but also autofix (provided that an autofix is available for them and is safe); indeed, there might be rules you would check against, but manually (and not automatically) fix ↩

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2e2ff0c) 100.00% compared to head (f785b9e) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #7   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           12        12           
  Lines          220       220           
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  Hits           220       220           

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