chore: Cleanup type hints

Description

Add type hints to the package.

When using the results I found the type-hints from pint unsatisfactory. It was casting all params to Quantity which isn't the case if None is provided. Now the verify_units decorator passes through the type-hint from the wrapped function. This isn't perfect, but a good balance on the effort/outcome scale for now.

I also noticed that everything is cast to a Quantity so the python-type conversion isn't really needed until pint enables the use of something like Quantity[float].

Merge Request Steps

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/.