I tried to make this look better, but failed. Please rename 'reference_implicit_mta_from_sta()' to maybe ensure_mta() or something like that, because apartments don't reference each other. We could definitely hide apt_cs use with some existing helpers, but it probably not that important. I'd remove tests for mismatching RoInit/RoUninit/CoInit/CoUninit, it does not look particularly relevant to what this MR is solving.