addset: promote to real smartset

Better revset performance are also achieved with less overlay. There is no good
reason for addset to not be a smartset. We can replace the `_orderedsetmixin`
inheritance since `abstractsmartset` has efficient min and max too.

mercurial/revset.py

@@ -2554,7 +2554,7 b' class orderedlazyset(_orderedsetmixin, f'
         self._subset.reverse()
         self._ascending = not self._ascending
 
-class _addset(_orderedsetmixin):
+class _addset(abstractsmartset):
     """Represent the addition of two sets
 
     Wrapper structure for lazily adding two structures without losing much