ruff

8198668f - [red-knot] MDTest: Use custom class names instead of builtins (#16269)

[red-knot] MDTest: Use custom class names instead of builtins (#16269) ## Summary Follow up on the discussion [here](https://github.com/astral-sh/ruff/pull/16121#discussion_r1962973298). Replace builtin classes with custom placeholder names, which should hopefully make the tests a bit easier to understand. I carefully renamed things one after the other, to make sure that there is no functional change in the tests.