tests: add a metaclass for triggering stupid on a class level We use a metaclass similar to the tests for obsolete mode. This metaclass deliberately duplicates each test for each mode; enabling both means that each test function is run four times. This makes it less likely that a fix is accidentally applied to replay mode only, as new tests will often automatically cover both modes. However, as certiain features remain deliberately unimplemented in stupid modes -- filemaps being a notable example -- we also add a decorator function for marking methods testing them. We do this for reasons of both consistency and coverage; we avoid littering the tests with *_stupid variants, and thus are less likely to forget adding them. I already found a couple of bugs in stupid mode thanks to this increased coverage.