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/router/httpTriggers.go

@@ -50,16 +50,18 @@ type HTTPTriggerSet struct {
 	*functionServiceMap
 	*mutableRouter
 
-	logger                     *zap.Logger
-	fissionClient              versioned.Interface
-	kubeClient                 kubernetes.Interface
-	executor                   eclient.ClientInterface
-	resolver                   *functionReferenceResolver
-	triggers                   []fv1.HTTPTrigger
-	triggerInformer            map[string]k8sCache.SharedIndexInformer
-	functions                  []fv1.Function
-	funcInformer               map[string]k8sCache.SharedIndexInformer
-	informerMu                 sync.RWMutex
+	logger          *zap.Logger
+	fissionClient   versioned.Interface
+	kubeClient      kubernetes.Interface
+	executor        eclient.ClientInterface
+	resolver        *functionReferenceResolver
+	triggers        []fv1.HTTPTrigger
+	triggerInformer map[string]k8sCache.SharedIndexInformer
+	functions       []fv1.Function
+	funcInformer    map[string]k8sCache.SharedIndexInformer
+	informerMu      sync.RWMutex
+	// nsCancels holds per-namespace context cancel functions for informer lifecycle.
+	nsCancels                  map[string]context.CancelFunc
 	updateRouterRequestChannel chan struct{}
 	tsRoundTripperParams       *tsRoundTripperParams
 	isDebugEnv                 bool
@@ -84,6 +86,7 @@ func makeHTTPTriggerSet(logger *zap.Logger, fmap *functionServiceMap, fissionCli
 		svcAddrUpdateThrottler:     actionThrottler,
 		unTapServiceTimeout:        unTapServiceTimeout,
 		syncDebouncer:              debounce.New(time.Millisecond * 20),
+		nsCancels:                  make(map[string]context.CancelFunc),
 	}
 	httpTriggerSet.triggerInformer = utils.GetInformersForNamespaces(fissionClient, time.Minute*30, fv1.HttpTriggerResource)
 	httpTriggerSet.funcInformer = utils.GetInformersForNamespaces(fissionClient, time.Minute*30, fv1.FunctionResource)
@@ -526,11 +529,39 @@ func (ts *HTTPTriggerSet) AddNamespace(ctx context.Context, ns string, mgr manag
 		ns + "/trigger": triggerInf,
 		ns + "/func":    funcInf,
 	})
-	factory.Start(ctx.Done())
+
+	// Create a per-namespace cancellable context for informer lifecycle.
+	nsCtx, nsCancel := context.WithCancel(ctx)
+	ts.nsCancels[ns] = nsCancel
+
+	factory.Start(nsCtx.Done())
 	// Wait for cache to sync before rebuilding the router, so triggers are visible.
-	k8sCache.WaitForCacheSync(ctx.Done(), triggerInf.HasSynced, funcInf.HasSynced)
+	k8sCache.WaitForCacheSync(nsCtx.Done(), triggerInf.HasSynced, funcInf.HasSynced)
 
 	ts.logger.Info("router.AddNamespace: done", zap.String("namespace", ns))
 	ts.syncTriggers()
 	return nil
 }
+
+// RemoveNamespace deregisters a namespace from the router.
+// Cancels the per-namespace informer context, removes informers from internal maps,
+// and triggers a syncTriggers so stale routes are removed immediately.
+func (ts *HTTPTriggerSet) RemoveNamespace(ns string) {
+	if ns == "" {
+		return
+	}
+	ts.logger.Info("router.RemoveNamespace: cleaning up namespace", zap.String("namespace", ns))
+
+	if cancel, ok := ts.nsCancels[ns]; ok {
+		cancel()
+		delete(ts.nsCancels, ns)
+	}
+
+	ts.informerMu.Lock()
+	delete(ts.triggerInformer, ns)
+	delete(ts.funcInformer, ns)
+	ts.informerMu.Unlock()
+
+	ts.syncTriggers()
+	ts.logger.Info("router.RemoveNamespace: done", zap.String("namespace", ns))
+}