@Override
  public long addNewUnverifiedForkchoiceListener(
      final UnverifiedForkchoiceListener unverifiedForkchoiceListener) {
    return newUnverifiedForkchoiceCallbackSubscribers.subscribe(unverifiedForkchoiceListener);
  }
Instantiates a new Post merge context.

@param difficulty the difficulty
consensus/merge/src/main/java/org/hyperledger/besu/consensus/merge/PostMergeContext.java