Use mypy for static type checking

### Describe the new feature

Currently mypy is not used in this project. For the scope of it, stability is of utmost importance and we should use a static type checker to avoid unnecessary TypeErrors at runtime.

Start by reviewing the repository's Python package and current development configuration to determine how mypy should be introduced. Check how development checks are currently run and define a repeatable mypy command. Done means static type checking is configured for the intended project scope and runs reliably without introducing unnecessary runtime changes.

Written by the indexing model from the issue text.