ReorgDetectorImpl

Implementation of ReorgDetector using in-memory block history.

Thread Safety: Uses Mutex for coroutine-safe operations.

Algorithm:

1. Maintain sliding window of recent blocks (map: height → BlockInfo)

2. When new block arrives, check if parent hash matches previous block

3. If mismatch, walk backwards to find common ancestor

4. Emit ReorgEvent with old and new branches

5. Update block history with new canonical blocks