* _default_manager has more specific type for TypeVars
* remove unnecessary # type: ignore
* add test for _base_manager
* add overloads for classproperty.__get__
* readd # type: ignore for WSGIRequestHandler.connection, fails in github's pipeline
* fix _base_manager test: mypy reveals an inferred type
Co-authored-by: Michael Pöhle <michael.poehle@polyteia.de>