macOS runner VM clocks are synced before jobs start to keep step and metric timestamps aligned

We now force an NTP sync on macOS runner VMs immediately after dispatch succeeds and before the job starts. Previously, a freshly booted VM could be handed a job before macOS timed had corrected a clock that started minutes behind, causing GitHub step timestamps and metrics timestamps to drift onto different timelines. This made early steps look missing or misaligned in the charts. The synchronous sntp step brings the guest clock in line before the runner and sampler start, so steps and metrics share one timeline.