[cse7766] Fix power reading stuck when load switches off

When the load is switched off and current drops below the chip's
measurable threshold (~50mA), the CSE7766 sets have_power=false
indicating no valid power measurement. The code was not publishing
any value in this case, leaving the power sensor stuck at its last
reading (e.g., 200W) for 10-20 seconds.

This regression was introduced in 2024.2.0 when PR #6180 refactored
the code from an accumulator-based design to direct publishing. The
original code handled this case by incrementing power_counts_ when
have_voltage && !have_power, effectively publishing 0W.

Fixes esphome/esphome#13613

esphome/components/cse7766/cse7766.cpp

@@ -152,6 +152,10 @@ void CSE7766Component::parse_data_() {
     if (this->power_sensor_ != nullptr) {
       this->power_sensor_->publish_state(power);
     }
+  } else if (this->power_sensor_ != nullptr) {
+    // No valid power measurement from chip - publish 0W to avoid stale readings
+    // This typically happens when current is below the measurable threshold (~50mA)
+    this->power_sensor_->publish_state(0.0f);
   }
 
   float current = 0.0f;