@Override
  public long subscribeInSync(final InSyncListener listener, final long syncTolerance) {
    return 0;
  }
Naive implementation of Synchronizer used by retesteth. Because retesteth is not implemented in
the test module, it has no access to mockito. This class provides a minimum implementation needed
to run RPC methods which may require a Synchronizer.
ethereum/core/src/test-support/java/org/hyperledger/besu/ethereum/core/DummySynchronizer.java