0138cd238a
Partially addresses https://github.com/astral-sh/ty/issues/1732 ## Summary Don't union the previous type in fixpoint iteration if the previous type contains a `Divergent` from the current cycle and the latest type does not. The theory here, as outlined by @mtshiba at https://github.com/astral-sh/ty/issues/1732#issuecomment-3609937420, is that oscillation can't occur by removing and then reintroducing a `Divergent` type repeatedly, since `Divergent` types are only introduced at the start of fixpoint iteration. ## Test Plan Removes a `Divergent` type from the added mdtest, doesn't otherwise regress any tests.