[api] Eliminate rx_buf heap churn and release buffers after initial sync (#12133)

esphome/components/api/api_connection.cpp

@@ -169,8 +169,7 @@ void APIConnection::loop() {
       } else {
         this->last_traffic_ = now;
         // read a packet
-        this->read_message(buffer.data_len, buffer.type,
-                           buffer.data_len > 0 ? &buffer.container[buffer.data_offset] : nullptr);
+        this->read_message(buffer.data_len, buffer.type, buffer.data);
         if (this->flags_.remove)
           return;
       }
@@ -195,6 +194,9 @@ void APIConnection::loop() {
       }
       // Now that everything is sent, enable immediate sending for future state changes
       this->flags_.should_try_send_immediately = true;
+      // Release excess memory from buffers that grew during initial sync
+      this->deferred_batch_.release_buffer();
+      this->helper_->release_buffers();
     }
   }