temp: Toggle pico led as heatbeat

To show that the monitor is alive, blink the onboard LED of the pico.

Misc/Temp-Monitor/temperature_monitor.py

@@ -6,6 +6,8 @@ from machine import Pin
 
 clock = Pin(2)
 data = Pin(4)
+led = Pin(25, Pin.OUT)
+led.high()
 
 ADC_RATE = 40
 
@@ -50,5 +52,6 @@ while True:
         if elapsed >= 200 or elapsed < 0:
             print(f"{temperature:.6f},{temperature_filtered:.6f}")
             last_report = now
+            led.toggle()
     except Exception as e:
         print(f"Error {e}")