addset: drop `.set()` usage during iteration

We can use the containment check directly.

mercurial/revset.py

@@ -2541,9 +2541,9 b' class addset(abstractsmartset):'
             def gen():
                 for r in self._r1:
                     yield r
-                s = self._r1.set()
+                inr1 = self._r1.__contains__
                 for r in self._r2:
-                    if r not in s:
+                    if not inr1(r):
                         yield r
             gen = gen()
         else: