Adopt pyproject.toml standard, fast-forward cookiecutter

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes Mettre à jour les instructions d'installation #44
  • This PR also addresses a longstanding objective to modernize the packaging standards
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• HISTORY.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Uses the latest cookiecutter template
• Replaces setup.py, MANIFEST.in, and configs in the setup.cfg for pyproject.toml and .flake8
• Most flake8 checks are now handled via ruff
• New GitHub Workflows for automatically managing version bump and actions versions.
• Documentation adjustments

Does this PR introduce a breaking change?

Yes. We now are using pyproject.toml with flit to build the library. This will entail one or two major changes to a typical development workflow.

The main changes worth noting:

• $ pip install -e . should be substituted for $ flit install -s/--symlink . when performing development installations ($ pip install . works exactly as you'd expect).
  • Alternatively, one can run $ make develop. This is documented.
• Most configurations are now found within the pyproject.toml

Other information:

https://flit.pypa.io/en/stable/index.html
https://peps.python.org/pep-0518/
https://peps.python.org/pep-0621/
https://www.mypy-lang.org/

[RondeauG]

Great job, thanks!

[RondeauG]

We'll need to modify PULL_REQUEST_TEMPLATE.md to refer to CHANGES.rst, instead of HISTORY.rst