Add TODO

VersionedMap.cpp

@@ -827,6 +827,8 @@ VersionedMap::Iterator::operator=(Iterator &&other) noexcept {
   return *this;
 }
 
+// TODO once we have good testing for this, design a state machine that fuses
+// adjacent point and range clears at the same version.
 VersionedMap::Iterator::VersionedMutation
 VersionedMap::Iterator::operator*() const {
   assert(impl->finger.backNode() != 0);