Cleanup imageruler codebase

[ianwilliamson]

This PR is a first step at cleaning up the imageruler codebase. Summary of changes:

• Apply common formatting to the primary modules
• Add missing type hints and fix inconsistencies
• Clean up docstrings
• Remove unecessary docstrings on private functions
• Add a padding mode enum

Overall, this is just a starting point. There is still a lot of ambiguity in some of the docstrings around default values and expected behaviors, e.g. what happens when phys_size is not specified

[stevengj]

LGTM.