Static typing for Python code - mypy

[pcaversaccio]

We should implement a static type checker for our Python code. Python is a dynamic language, so usually, we will only see errors in our code when you attempt to run it. mypy is a static checker, so it finds bugs in our programs without even running them.

We need the following:

• GitHub Action for mypy: https://github.com/jpetrucciani/mypy-check
• pre-commit hook: https://github.com/pre-commit/mirrors-mypy