lazyset: inherit the fastasc and fastdesc method from subset

When the filtered subset has such methods, we can use them. It is implemented
as properties to be able to quickly return None if no corresponding fastasc exists
on the subset.

mercurial/revset.py

@@ -2444,6 +2444,20 b' class lazyset(abstractsmartset):'
             if cond(x):
                 yield x
 
+    @property
+    def fastasc(self):
+        it = self._subset.fastasc
+        if it is None:
+            return None
+        return lambda: self._iterfilter(it())
+
+    @property
+    def fastdesc(self):
+        it = self._subset.fastdesc
+        if it is None:
+            return None
+        return lambda: self._iterfilter(it())
+
     def __and__(self, x):
         return lazyset(self, x.__contains__)