Function collection_insert

cpp/fory/serialization/collection_serializer.h:402–408

// Helper to insert element into container (vector or set)
template <typename Container, typename T>
inline void collection_insert(Container &result, T &&elem) {
  if constexpr (has_push_back_v<Container, T>) {
    result.push_back(std::forward<T>(elem));
  } else {
    result.insert(std::forward<T>(elem));
  }
}

/// Read collection data for polymorphic or shared-ref elements.
template <typename T, typename Container>