Only nose.tools was used, which can easily be replaced with one-liners and pytest.raises

See https://mypy.readthedocs.io/en/stable/installed_packages.html#creating-pep-561-compatible-packages for how to opt-in to mypy type checking in user code.

Add type hints to models.py

See merge request !67

F mypy

See merge request !66

Add Python 3.12 to tests

See merge request !132

- Replaces nose