fix(namespace): executor/router/buildermgr RemoveNamespace + per-NS informer lifecycle

- Add RemoveNamespace(ctx, ns) to executortype.ExecutorType interface
- Implement RemoveNamespace in poolmgr, newdeploy, container executor types
- Add per-namespace context cancellation (nsCancels map) in all three types so
  informer factories are stopped when namespace is removed (fixes goroutine leak)
- Add PoolPodController.RemoveNamespace to clear envLister/podLister maps
- Add deregisterNamespace() in executor multitenant subscriber
- Switch executor/router/buildermgr watcher strategy from TrackOnly to DispatchRemove
  so RemoveFunc is called when fission.io/managed label is removed
- Add RemoveFunc to executor/router/buildermgr namespace subscribers
- Add RemoveNamespace to environmentWatcher and packageWatcher with per-NS cancel
- Add RemoveNamespace to HTTPTriggerSet: cancels informers, removes from maps, calls syncTriggers
- Fix ns_watcher_test.go fakeExecutorType to implement new RemoveNamespace method

Fixes:
- Executor dedup gap: re-added namespace was silently skipped (envLister/deplLister still present)
- Goroutine/FD leak: old informer factories ran forever after namespace removal
- Router stale routes: HTTPTriggers for removed namespace stayed in routing table

pkg/buildermgr/pkgwatcher.go

@@ -49,6 +49,8 @@ type (
 		pkgInformer   map[string]k8sCache.SharedIndexInformer
 		storageSvcUrl string
 		buildCache    *cache.Cache[crd.CacheKeyUR, *fv1.Package]
+		// nsCancels holds per-namespace context cancel functions.
+		nsCancels map[string]context.CancelFunc
 	}
 )
 
@@ -64,6 +66,7 @@ func makePackageWatcher(logger *zap.Logger, fissionClient versioned.Interface, k
 		pkgInformer:   pkgInformer,
 		storageSvcUrl: storageSvcUrl,
 		buildCache:    cache.MakeCache[crd.CacheKeyUR, *fv1.Package](0, 0),
+		nsCancels:     make(map[string]context.CancelFunc),
 	}
 	return pkgw
 }
@@ -363,7 +366,23 @@ func (pkgw *packageWatcher) AddNamespace(ctx context.Context, ns string, mgr man
 		ns + "/pkg": pkgInf,
 		ns + "/pod": podInf,
 	})
-	fissionFactory.Start(ctx.Done())
-	podFactory.Start(ctx.Done())
+
+	// Create a per-namespace cancellable context for informer lifecycle.
+	nsCtx, nsCancel := context.WithCancel(ctx)
+	pkgw.nsCancels[ns] = nsCancel
+
+	fissionFactory.Start(nsCtx.Done())
+	podFactory.Start(nsCtx.Done())
 	pkgw.logger.Info("buildermgr.pkgWatcher.AddNamespace: done", zap.String("namespace", ns))
 }
+
+// RemoveNamespace deregisters a namespace from the package watcher.
+func (pkgw *packageWatcher) RemoveNamespace(ns string) {
+	if cancel, ok := pkgw.nsCancels[ns]; ok {
+		cancel()
+		delete(pkgw.nsCancels, ns)
+	}
+	delete(pkgw.pkgInformer, ns)
+	delete(pkgw.podInformer, ns)
+	pkgw.logger.Info("buildermgr.pkgWatcher.RemoveNamespace: cleaned up", zap.String("namespace", ns))
+}