feat(metadata): Add OSS-CRS phase timestamps

[fuyu0425]

Summary

• Add Unix timestamp metadata fields for OSS-CRS build/run phase boundaries in metadata models and metadata.json persistence.
• Capture build/run start and end timestamps in the OSS-CRS adapter and thread authoritative run start timing through runner callbacks.
• Preserve matching ISO timestamp and timestamp_unix values across worker metadata, orchestrator fallback metadata, and legacy metadata reconstruction.
• Document the new trial timing metadata fields.

Testing

• uv run pytest tests/test_orchestrator_markers.py::TestWriteOrchestratorMarker::test_metadata_fallback_derives_unix_from_existing_iso_timestamp tests/test_orchestrator_markers.py::TestWriteOrchestratorMarker::test_metadata_fallback_writes_iso_timestamp_from_unix tests/test_orchestrator_markers.py::TestWriteOrchestratorMarker::test_metadata_contains_phase_timestamp_fields -q
• uv run pytest tests/test_orchestrator_markers.py tests/test_e2e_compose_bugfind.py tests/test_execution_timing.py tests/test_compose_adapter.py -q
• uv run ruff format crsbench/ tests/
• scripts/ci-tests/run-local.sh checks

Notes

• Final agent re-review reported no findings.
• Untracked local files .gitignore.local and target.org were intentionally left out.