Added ensureMetadataVisible() method that:
- Performs lookup after flush to verify metadata is visible
- Retries with exponential backoff if metadata is stale
- Logs all attempts for debugging
STATUS: Method is being called but EOF error still occurs.
Need to investigate:
1. What metadata values are being returned
2. Whether the issue is in write or read path
3. Timing of when Spark reads vs when metadata is visible
The method is confirmed to execute (logs show it's called) but
the 78-byte EOF error persists, suggesting the issue may be
more complex than simple metadata visibility timing.