Build archives with machine metrics no longer sink build processing

The run-metrics and build-insights pipeline no longer drops builds because the live machine_metrics.jsonl (written every second by the always-on tuist.metrics-sampler LaunchDaemon) was captured mid-write and produced a bad-CRC archive entry. The metrics file is now snapshotted under the sampler’s file lock when a build archive is bundled, exactly like the existing read path uses.