@Override
  protected long cacheFreeSpace() {
    return Integer.MAX_VALUE;
  }
Returns pending txs by sender and ordered by score desc. In case a sender has pending txs with
different scores, then in nonce sequence, every time there is a score decrease, his pending txs
will be put in a new entry with that score. For example if a sender has 3 pending txs (where
the first number is the nonce and the score is between parenthesis): 0(127), 1(126), 2(127),
then for he there will be 2 entries:

<ul>
  <li>0(127)
  <li>1(126), 2(127)
</ul>

@return pending txs by sender and ordered by score desc
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/layered/AbstractPrioritizedTransactions.java