General refactor and code improvements, v2

[philippfriese]

This PR (again):

• adds first round of type hints throughout the project (partially resolved #13)
• adds several changes from raw file handlers to context managed file objects
• normalises code comments to adhere to PEP 8
• changes potentially static methods to "real" static methods using @staticmethod
  • this more strongly expresses the intent that the static method does not modify parent class members
• improves exception messages by adding exception strings
• adds several TODO comments to places where
  • a match statement could be used one Python >=3.10 is used
  • parameters are not used
  • signatures of base classes are not adhered by