Test and lint all the nox commands

[Carreau]

See #1962

It looks like some of the nox commands have been broken for a while.

This should be tested/linted in CI.

I also realized we don't run typechecker like mypy on the codebase – yes this is a theme, and docutils might trigger a number of false-positive but I think we should still add mypy.

[trallard]

+1 on using mypy - we are moving away from nox. I just had not gotten around to moving the translation bits to tox, but this should be done in #1959

So let's close this issue and open one for mypy checks