Add comment explaining early guard

esphome/components/tuya/tuya.cpp

@@ -31,6 +31,8 @@ void Tuya::setup() {
 }
 
 void Tuya::loop() {
+  // Early return avoids stack adjustment for the batch buffer below.
+  // loop() runs ~7000/min so most calls have nothing to read.
   int avail = this->available();
   if (avail > 0) {
     // Read all available bytes in batches to reduce UART call overhead.