Make tests that wait for concurrent work wait on the event or a condition with a long deadline (issue 1814)

A test that slept a fixed time and then asserted what a goroutine, process or
watcher did failed under the checker's load. Each now waits for its positive
evidence (a started baseline, a call counted, a state reached) within 30 s, and
the concurrency-limit tests meet at a barrier instead of overlapping by sleep.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/dbus/cmd/dbus-tools/watcher_test.go

@@ -422,11 +422,11 @@ func TestRunWithoutABusSaysItStalledAndReconnects(t *testing.T) {
 	}, nil)
 	w.state = filepath.Join(t.TempDir(), "bus")
 	w.retry = 20 * time.Millisecond
-	ctx, cancel := context.WithTimeout(context.Background(), 6*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), 40*time.Second)
 	defer cancel()
 	done := make(chan struct{})
 	go func() { w.Run(ctx); close(done) }()
-	deadline := time.Now().Add(6 * time.Second)
+	deadline := time.Now().Add(30 * time.Second)
 	for time.Now().Before(deadline) && !w.Snapshot().Connected {
 		time.Sleep(50 * time.Millisecond)
 	}