Overhaul using scientific-python cookie

[smithara]

Implements a modern package development setup by applying the scientific-python cookie recipe.

It is applied using copier and can be updated with e.g.:

pipx install copier
pipx inject copier copier-templates-extensions
copier update --trust

or re-applied with copier copy gh:scientific-python/cookie . --trust

(but check the instructions from the cookie repo and from copier)

To do:

• decide how change log should be handled

To do after merging:

• set 2.1.0 as the git tag; verify the package still works as expected; test the release process, then enable pushing to real pypi
• Re-enable skipped checks, one at a time, and fix the code for them:
  • Typing (mypy)
  • Linting with Ruff
  • Other stuff like the spell checker
• Set up readthedocs and a minimal documentation

sp-repo-review validates the repo, e.g. https://learn.scientific-python.org/development/guides/repo-review/?repo=smithara%2Fppigrf&branch=use-scientific-python-cookie