message: Improve usability of FieldValues
diff: @@ -54,11 +54,19 @@ public:
  FieldValues() {}
  FieldValues(std::initializer_list<FieldValue>);
  void insert(ColKey k, Mixed val, bool is_default = false);
  - auto begin() const
  + auto begin() const noexcept
  {
  return m_values.begin();
  }
  - auto end() const
  + auto end() const noexcept
  + {
  + return m_values.end();
  + }
  + auto begin() noexcept
  + {
  + return m_values.begin();
  + }
  + auto end() noexcept
  {
  return m_values.end();
  }
  