Python: mypy coverage for the smaller folders

[eavanvalkenburg]

Motivation and Context

Extend mypy coverage for three of the smaller folders still to go

Description

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile: