fix(prometheus): clean up default Prometheus metric collectors on stop

ts/smartmetrics.classes.smartmetrics.ts

@@ -22,10 +22,11 @@ export class SmartMetrics {
   // HTTP server for Prometheus endpoint
   private prometheusServer?: plugins.http.Server;
   private prometheusPort?: number;
+  private cleanupDefaultMetrics?: () => void;
 
   public setup() {
     this.registry = new plugins.prom.Registry();
-    plugins.prom.collectDefaultMetrics(this.registry);
+    this.cleanupDefaultMetrics = plugins.prom.collectDefaultMetrics(this.registry);
 
     // Initialize custom gauges
     this.cpuPercentageGauge = new plugins.prom.Gauge({
@@ -295,5 +296,9 @@ export class SmartMetrics {
   public stop() {
     this.started = false;
     this.disablePrometheusEndpoint();
+    if (this.cleanupDefaultMetrics) {
+      this.cleanupDefaultMetrics();
+      this.cleanupDefaultMetrics = undefined;
+    }
   }
 }