typing: add trivial type hints to `mercurial.scmutil`
There's still a lot to go, but there's a lot here already, so I tried to keep it
to obvious/trivial things. I didn't bother with contexts, matchers, and
revisions that can be `bytes | int | None`.
public attribute not declared in interfaces: badpeer.badattribute
public attribute not declared in interfaces: badpeer.badmethod