@Override
  public Stream<Pair<byte[], byte[]>> streamFromKey(
      final SegmentIdentifier segmentId, final byte[] startKey) {
    final Bytes startKeyBytes = Bytes.wrap(startKey);
    return stream(segmentId).filter(e -> startKeyBytes.compareTo(Bytes.wrap(e.getKey())) <= 0);
  }
Constructor which takes an explicit backing map for the layered key value storage.

@param map the backing map
@param parent the parent key value storage for this layered storage.
services/kvstore/src/main/java/org/hyperledger/besu/services/kvstore/LayeredKeyValueStorage.java