[CI/CD] Add mypy to CI

[RNKuhns]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is.

It would be nice to add mypy to the project's CI suite.

Describe the solution you'd like
A clear and concise description of what you want to happen, ideally taking into consideration the existing toolbox design, classes and methods.

Use pre-commit to add mypy to the project.

Additional context
I did not implement this initially, b/c there are currently a handful of mypy typing issues that need to be sorted out.

[fkiraly]

obsolete