It's another huge but fairly basic changeset: ruff has a LOT of opinions, and the great majority of the commit "Ruff for all test files" is mechanical application of what ruff wants. In some cases I've reworded comments to make the line length happier or to clean up grammar. I've done ruff's recommendations of replacing all the os file operations with Path operations. I've changed all the type stuff for Optional and Union to using pipe-separated typing declarations. It still passes its unit tests (although I have not rolled up my sleeves to attempt replacing pytest-vcr with something more maintainable).