v1.4.20

chore: Release v1.4.20 — demote [trace] log flood to DEBUG

P0 of the macula-relay refactor plan. The diagnostic tracing added
during the 1.4.16–1.4.19 cross-relay PONG investigation was shipping
at INFO and flooding production at thousands of events/second.

- Firehose sites (quic_data, frame type_id, PING send, PONG recv,
  ignoring frame, streams_available, peer_needs_streams) → DEBUG
- [trace] prefix dropped on remaining logs
- UNHANDLED handle_info stays INFO; peer new_stream stays WARNING
- stream-open setopt trace deleted outright

No behavior change.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>