Fold a List attribute's ElementDataType into the hashable projection so a
change to the element type (e.g. Int32 -> Double) with identical JSON-encoded
values is detected as a staleness/revision change. Inserted in alphabetical
position; null ElementDataType (scalars) is omitted by the canonical
serializer (WhenWritingNull), so scalar-only configs hash identically to
before. DiffService.AttributesEqual gains the same comparison to keep the
structured diff in parity with the staleness hash. Adds tests for differing
vs. equal ElementDataType (hash + diff) and the scalar no-op guard.
Joseph Doherty
5185486a3c