Add static typechecker to pre-commits and tests

[mmschlk]

We should add mypy static type checking. This will however need some changes in what typehints we currently are using. Especially there will be problems/changes with current np.ndarry[int] kind of hints.

• Add mypy support to pre-commits
• Adjust codebase typehints to make mypy test green
• Add mypy test to CI this should be done after or also in Add Codestyle Test to CI #45
• Edit description in CONTRIBUTING.md

[mmschlk]

While this is an important issue it may be out of scope for the initial version of SHAPIQ