Add a replay fixture for Binance candlestick WebSocket messages that exercises the gap detector.
Acceptance criteria:
- Include normal, missing-sequence, duplicate, and stale-heartbeat scenarios.
- Test that gaps are detected without panics.
- Keep fixtures small and redacted; no credentials.
- Link the test to the ingestion gap-detector behavior.
Add a replay fixture for Binance candlestick WebSocket messages that exercises the gap detector.
Acceptance criteria: