Add type hints and docstrings to python IO file

[johnwlambert]

Currently the read_write_model.py file is not very clear because the input and return types are not explained thoroughly. This PR updates the documentation for scripts/python/read_write_model.py .

• Reformatted docstrings to be consistent and in the google format (https://google.github.io/styleguide/pyguide.html#383-functions-and-methods)
• Added type hints to improve readability.
• Reformatted code in the python black style for consistency.