message: Use binary search in Set::find()
diff: @@ -264,7 +264,13 @@ Set<U> Obj::get_set(ColKey col_key) const
  template <class T>
  size_t Set<T>::find(T value) const
  {
  - return m_tree->find_first(value);
  + auto b = this->begin();
  + auto e = this->end();
  + auto it = std::lower_bound(b, e, value, SetElementLessThan<T>{});
  + if (it != e && SetElementEquals<T>{}(*it, value)) {
  + return it.index();
  + }
  + return npos;
  }
  template <class T>
  