Count the take-ins and every other background work in the serving group, so serve's stop waits for them too (issue 1945)

inBackground ran the take-ins of done keys (now in #463's slots), the start's
look, the given values' replacement and the announced reads beside serve without
serve waiting for them: a take-in could outlive its controller as the loops did.
It now takes the context and is counted in its serving group as well, and a
serve that is stopping starts none.

cmd/mesh-controller/states_announced.go

@@ -67,7 +67,7 @@ func keepAnnouncements(ctx context.Context, js *broker.JetStream, open *stores)
 			return
 		}
 		if changed {
-			inBackground(func() { composeAnnouncedReads(context.WithoutCancel(ctx), open) })
+			inBackground(ctx, func() { composeAnnouncedReads(context.WithoutCancel(ctx), open) })
 		}
 	})
 	if err != nil {