Runner image syncs clock before jobs so metrics charts align with steps

macOS runner images now synchronize their clock with NTP before starting a job. This prevents the runner VM’s boot-skewed clock from stamping GitHub step timestamps minutes earlier than the machine metrics, so the runner-job metrics charts now align correctly with the step timeline and step-hover highlights land on the right region of the graph. The sync is best-effort and runs after the job is dispatched, before the runner and metrics sampler start. This only affects the macOS runner image; Linux VMs already receive an accurate paravirt clock at boot.