message: Add missing function overload
diff: @@ -226,6 +226,10 @@ public:
  return emplace_hint(hint, key, std::forward<T>(value));
  }
  + void insert(const_iterator first, const_iterator last) {
  + xs_.insert(first, last);
  + }
  +
  template <class T>
  iterator_bool_pair insert_or_assign(string_view key, T&& value) {
  auto i = lower_bound(key);
  