Break out mypy

[TomAugspurger]

Moves mypy out of pre-commit and into a separate CI check.

[kylebarron]

I'm still quite confused by hatch. This will use the hatch env? Even without running something like hatch run mypy .?

[TomAugspurger]

Mmm I don't use any hatch commands directly locally. My shell automatically activates the virtulaenv when I cd into the directory.

In the case of the GHA, I don't think there's a virtulenv at all. Just running stuff in some python interpreter.

I think our only hard requirement on using hatch is at build time (and even that is hidden by python -m build ., which figures out how to use hatch for building the wheel and sdit based on the metadata in pyproject.toml).

But in general: we need a contributing guide.

[kylebarron]

I see. I'm a big fan of Poetry and Pixi but have never used hatch before, so I'm learning it.

[TomAugspurger]

I like it, in that there's (ideally) nothing new to learn if you don't want to :)