@Override
  protected long cacheFreeSpace() {
    return poolConfig.getPendingTransactionsLayerMaxCapacityBytes() - getLayerSpaceUsed();
  }
Order sparse tx by priority flag and sequence asc, so that we pick for eviction txs that have
no priority and with the lowest sequence number (oldest) first.
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/layered/SparseTransactions.java