@Override
  protected boolean promotionFilter(final PendingTransaction pendingTransaction) {
    return false;
  }
We only want to promote transactions that have gap == 0, so there will be no gap in the prev
layers. A promoted transaction is removed from this layer, and the gap data is updated for its
sender.

@param promotionFilter the prev layer's promotion filter
@param freeSpace max amount of memory promoted txs can occupy
@param freeSlots max number of promoted txs
@return a list of transactions promoted to the prev layer
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/layered/SparseTransactions.java