ci(python): Run mypy as part of the lint workflow

[stinodego]

Changes:

• Add separate jobs in the lint workflow for running mypy on Python 3.7 and 3.11.
• The part that of that workflow that lints the Rust code (rustfmt and clippy) is now a separate job

Advantages:

• If there is a mypy error, we still get to see whether our tests pass.
• It makes sense for mypy to be run as part of the lint workflow
• With the Rust part separated out, the overall runtime of the lint job is now about 30 seconds shorter. (which doesn't matter much, as the Windows test workflow is the bottleneck)

Disadvantages:

• Costs slightly more compute to run things this way, as we have to install dev dependencies twice. This is hopefully offset by the fact that people will require fewer iterations to pass all workflows, as test failures become apparent more quickly.

[ritchie46]

Seems fine by me. 👍 I don't believe contention of workers is that high yet.

[stinodego]

All right, then it's going in! Let me know if any issues arise.