message: [storage] Improve iterators during TXN Commit
  Summary:
  There is no need to create vectors and zip them all together
  at the end; just zip directly with the transactions.
  Test Plan:
  cargo test; CI
diff: @@ -430,23 +430,10 @@ impl LibraDB {
  .put_transaction(ver, txn_to_commit.signed_txn(), &mut cs)
  })
  .collect::<Result<()>>()?;
  - let txn_hashes = txns_to_commit
  - .iter()
  - .map(|txn_to_commit| txn_to_commit.signed_txn().hash())
  - .collect::<Vec<_>>();
  - let gas_amounts = txns_to_commit
  - .iter()
  - .map(TransactionToCommit::gas_used)
  - .collect::<Vec<_>>();
  // Transaction accumulator updates. Get result root hash.
  - let txn_infos = izip!(
  - txn_hashes,
  - state_root_hashes,
  - event_root_hashes,
  - gas_amounts
  - )
  - .map(|(t, s, e, g)| TransactionInfo::new(t, s, e, g))
  + let txn_infos = izip!(txns_to_commit, state_root_hashes, event_root_hashes)
  + .map(|(t, s, e)| TransactionInfo::new(t.signed_txn().hash(), s, e, t.gas_used()))
  .collect::<Vec<_>>();
  assert_eq!(txn_infos.len(), txns_to_commit.len());
  