Add Typing to Project

[aenglander]

The project should support proper typing like the rest of the Pallets projects

See other Pallets projects

• Add Typing to classes and functions
• Add typing environment with mypy and pyright tests to tox
• Add a run in Gitlab actions

[davidism]

Start with mypy with strict=False. Once all those messages are addressed, again with strict=True. Then with pyright and pyright --verifytypes.

[Abdur-rahmaanJ]

• mypy strict false