Benchmark harness: fold post-check failures into the lane status

In a multi-lane benchmark driver, a timed lane can report status OK and the driver DONE rc 0 even though the measured output was never produced. The lane runner records only whether the timed command finished. The output checks (writer success flag, verify rc, file present) run later as separate post steps and only write their own logs. Anyone, human or script, who reads lane.json then treats a failed run as a valid timing row. Make the authoritative lane/run status the AND of the timed step and every required post (capture success, verify rc 0, output exists), and add a red stub case where a post fails but the timed step succeeds. Then nobody can quote elapsed time from a row whose output failed.