typing: (mostly) align the signatures of `imanifestrevisionstored` overrides When we change the implementations to subclass this explicitly, pytype complains that the signatures mismatch for various methods. It seems hung up on ones in `mercurial.manifest` that have type hints on the return value, but lacked it in the Protocol class (which it thinks returns `None` if there's no annotation). The tricky part is that a lot of the return types in the `mercurial.manifest` module are custom types specific to that module (e.g. `'manifestctx' | 'treemanifestctx'`). Those should probably be replaced with Protocol classes. I was going to avoid making a long series longer by disabling that check for now by putting `Any` as the return type on the Protocol class methods, and then realized the problem is the class isn't marked as a Protocol (that property isn't inherited). For now, lock in the synchronized signatures.