[api] Fix batch messages stuck in Nagle buffer (#15581)

esphome/components/api/api_connection.h

@@ -662,6 +662,7 @@ class APIConnection final : public APIServerConnectionBase {
   // Helper methods for iterator lifecycle management
   void destroy_active_iterator_();
   void begin_iterator_(ActiveIterator type);
+  void finalize_iterator_sync_();
 #ifdef USE_CAMERA
   std::unique_ptr<camera::CameraImageReader> image_reader_;
 #endif