Modernize packaging

[esoteric-ephemera]

Had difficulty installing the contribs client without using --config-settings editable_mode=compat. This PR just:

• Migrates the all namespace setup.py to a pyproject.toml
• Updates the precommit (didn't run since this is a huge diff on its own) to replace deprecated pragma with pyupgrade
• Adds check for MP_API_KEY in env to allow users to set only one common API key
• Replace long-deprecated CodeQL v1 with v4
• Close #1858 by permitting NaN to dimensionless (str()) unit conversion

Didn't migrate setup.py --> pyproject.toml for namespaces which aren't published to pypi, but happy to do so if that's useful

[esoteric-ephemera]

@tschaume this should be more or less ready. To make sure everything is still working once deployed, can I try this out on a local deployment, or would the change from datetime to semantic versioning make that impossible (guessing the server is still using datetime)?

[tschaume]

Thanks much, @esoteric-ephemera! Looks great! Other than a small comment, I think you can go ahead and try this in a local docker-compose stack with an rc version. I don't think the change in version format should be a problem - I can't recall why I decided on date-formatted versioning, maybe only because I wanted to automatically see when the new API was deployed the last time. It never really worked well and isn't needed anymore these days.