The test assumed msleep(100) measures close to 100 ms (expecting ~2
frames at 24fps vs ~6 at 60fps). On the loaded macOS CI runner the
24fps leg overslept ~2.5x, producing 6 frames at both rates. Measure
the actual interval per leg and compare against the expected frame
count with a 1-frame tolerance, and use highly distinct timebases
(1fps vs 240fps) for the rate-ordering check.