typing: add type annotations to mercurial/utils/dateutil.py For now, I'm just typing around the edges to help find issues with TortoiseHg. If the custom `hgdate` type is useful elsewhere as I go, I'll move it to a file dedicated to custom types. I'm not loving the ban on camelcase type names here that test-check-code.t flagged, but I'm not sure how to disable that even if everyone agreed that it's a bad idea to go against the normal convention for types. While here, fix an issue that pytype found in `parsedate` when an invalid date tuple is passed by raising a ProgrammingError instead of crashing. (Tuple doesn't have a `strip` attribute.) Differential Revision: https://phab.mercurial-scm.org/D10123