feat(api): total wait time in request metrics

[delong3]

Summary by cubic

Adds total wait time to scrape request metrics to improve observability of request delays. This exposes a new metric and includes it in the emitted metrics for both v1 and v2 controllers.

• New Features
  • Emit scrape.total_wait_time_ms in v2 telemetry.
  • Include totalWait in the metrics payload for v1 and v2 scrape controllers.

^{Written for commit 1295c48. Summary will update automatically on new commits.}

[cubic-dev-ai]

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