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/docker-compose/cmd/docker-compose-tools/jobs_test.go

@@ -43,8 +43,12 @@ func TestJobsASlowActIsAnsweredRunningWithItsID(t *testing.T) {
 		t.Fatalf("%+v", j)
 	}
 	close(release)
-	time.Sleep(50 * time.Millisecond)
-	got, _ := jobByID(j.ID)
+	var got Job
+	for end := time.Now().Add(30 * time.Second); time.Now().Before(end); time.Sleep(5 * time.Millisecond) {
+		if got, _ = jobByID(j.ID); !got.Running {
+			break
+		}
+	}
 	if got.Running {
 		t.Fatalf("finished afterwards: %+v", got)
 	}