@Override
    public Iterator<Address> iterator() {
      return Iterables.concat(prioritySenders, standardSenders).iterator();
    }
Return the full content of this layer, organized as a list of sender pending txs. For each
sender the collection pending txs is ordered by nonce asc.

<p>Returned sender list order detail: first the sender of the tx that will be evicted as last.
So for example if the same sender has the first and the last txs in the eviction order, it will
be the first in the returned list, since we give precedence to tx that will be evicted later.

@return a list of sender pending txs
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/layered/SparseTransactions.java