feat(abstract-utxo): make transaction explanation fields optional

Allow fee and locktime to be undefined in transaction explanations, improving
flexibility for edge cases.

Issue: BTC-2732

Co-authored-by: llm-git <[email protected]>

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -200,8 +200,8 @@ export function isWalletOutput(output: Output): output is FixedScriptWalletOutpu
   );
 }
 
-export interface TransactionExplanation extends BaseTransactionExplanation<string, string> {
-  locktime: number;
+export interface TransactionExplanation extends BaseTransactionExplanation<string | number | undefined, string> {
+  locktime?: number;
   /** NOTE: this actually only captures external outputs */
   outputs: Output[];
   changeOutputs: Output[];

modules/abstract-utxo/src/offlineVault/TransactionExplanation.ts

@@ -13,7 +13,7 @@ export interface TransactionExplanation {
   changeOutputs: ExplanationOutput[];
   fee: {
     /* network fee */
-    fee: string | number;
+    fee: string | number | undefined;
     payGoFeeString: string | number | undefined;
     payGoFeeAddress: string | undefined;
   };

modules/abstract-utxo/src/transaction/fixedScript/explainTransaction.ts

@@ -345,7 +345,7 @@ export function explainPsbt(
     inputSignatures: inputSignaturesCount,
     signatures: inputSignaturesCount.reduce((prev, curr) => (curr > prev ? curr : prev), 0),
     messages,
-  } as TransactionExplanation;
+  };
 }
 
 export function explainLegacyTx<TNumber extends number | bigint>(
@@ -363,5 +363,5 @@ export function explainLegacyTx<TNumber extends number | bigint>(
     ...common,
     inputSignatures: inputSignaturesCount,
     signatures: inputSignaturesCount.reduce((prev, curr) => (curr > prev ? curr : prev), 0),
-  } as TransactionExplanation;
+  };
 }