[1/n] Optimize new tracing logger

[LucioFranco]

This implements two improvements to our new tracing logger.

• Inline the different formats so that the compiler can optimize the
  callsite as much as possible.
• Instead of allocating a string to represent the intermediate
  representation of the logs, we use a writer now to collect the log
  line as we visit the event.

---

Note

Monomorphizes legacy text/JSON log formatting and writes events directly to the output, refactoring setup to select concrete formatters and integrate OTEL.

• Logger performance/structure:
  • Introduces LegacyFormatter trait with concrete TextFormatter and JsonFormatter that write directly to a Write target (no intermediate String).
  • Replaces LegacyFormatLayer<W> with LegacyFormatLayer<W, F> generic over formatter, enabling inlined, monomorphized on_event paths.
  • TextFormatter outputs fern-compatible text; JsonFormatter builds JSON via serde_json::to_writer.
  • New DirectWriteVisitor writes the message field directly; MessageVisitor simplified for JSON extraction.
• Setup refactor:
  • setup_legacy_format now matches on (format, export_to, stdout) to instantiate concrete formatters and writers (stdout or date-based file) and optionally attach OTEL via create_otel_layer.
  • Signature updated to use session_id/machine_id; session ID inclusion handled by formatter construction.

^{Written by Cursor Bugbot for commit cb1895c. This will update automatically on new commits. Configure here.}

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Preview	Comments	Updated (UTC)
docs-v2	Ready	Preview	Comment	Nov 26, 2025 9:52pm
framework-docs	Ready	Preview	Comment	Nov 26, 2025 9:52pm