fix: guard demo IIFE with require.main check

Prevents demo code from executing when module is required by Node-RED,
which caused crashes due to missing measurement data.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/specificClass.js

@@ -613,7 +613,8 @@ function pushSample(measurement, type, value, unit) { // eslint-disable-line no-
 }
 
 /** Demo *********************************************************************/
-(async function demoStationWithPump() {
+// Only run the demo when this file is executed directly (not when required as a module)
+if (require.main === module) (async function demoStationWithPump() {
   const station = new PumpingStation(createPumpingStationConfig("PumpingStationDemo"));
   const pump = new RotatingMachine(createMachineConfig("Pump1"), createMachineStateConfig());