chore: remove whitespace

[jsstevenson]

Cribbing description from https://github.com/biocommons/hgvs/pull/737

A lot of modern editors will auto-trim trailing whitespace upon save. Unfortunately, if there's a pesky space or two hanging around on some old file, then a new commit might create an unrelated edit on that line simply by making a functional change elsewhere in the file. This PR gets this out of the way for every .py file.