feat(api): usedLlm + formats in request metrics

[delong3]

Summary by cubic

Added usedLlm and formats to scrape request metrics to track when LLM processing is used and which formats were requested.

• New Features
  • usedLlm is true when formats include json, summary, branding (plus extract in v1), or changeTracking has json mode.
  • v1 logs formats directly from req.body.formats; v2 logs an array of format types derived from FormatObject.

^{Written for commit 1cc7b5b. Summary will update automatically on new commits.}

[cubic-dev-ai]

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