Add auxiliary function to get script from TxOut

Author: carlostome

src/Ledger/Dijkstra/Specification/Transaction.lagda.md

@@ -365,6 +365,10 @@ could be either of them.
 
   txinsScript : ℙ TxIn → UTxO → ℙ TxIn
   txinsScript txins utxo = txins ∩ dom (proj₁ (scriptOuts utxo))
+
+  txOutToScript : TxOut → Maybe Script
+  txOutToScript (_ , _ , _ , s) = s
+
 ```
 
 In the Dijkstra era, *spending* inputs must exist in the initial UTxO snapshot, while