DM XML parsing: Fix type annotations

Takes mypy errors down from 79 to 27. Nearly all remaining are
related to Enum - mypy has support for Enum functions, but it seems
like the derived classes are messing it up. Can be addressed
in a followup - this is still better.

The goal here is mostly to tighten up the type annotations and
move int -> uint for ids where possible, such that the spec
parsing is providing data with a stronger guarantee.

Testing: Tested by TestSpecParsing.py and TestSpecParsingDeviceTypes.py
         Also used by tests run in CI (including above)