refactor(abstract-utxo): make BaseParsedTransaction generic over TOutput

The regular `ParsedTransaction` type was a bit silly

Issue: BTC-1450

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -125,21 +125,21 @@ export interface VerifyAddressOptions<TCoinSpecific extends UtxoCoinSpecific> ex
   coinSpecific?: TCoinSpecific;
 }
 
-export interface BaseOutput {
+export interface BaseOutput<TAmount = string | number> {
   address: string;
-  amount: string | number;
+  amount: TAmount;
   // Even though this external flag is redundant with the chain property, it is necessary for backwards compatibility
   // with legacy transaction format.
   external?: boolean;
 }
 
-export interface FixedScriptWalletOutput extends BaseOutput {
+export interface FixedScriptWalletOutput<TAmount = string | number> extends BaseOutput<TAmount> {
   needsCustomChangeKeySignatureVerification?: boolean;
   chain: number;
   index: number;
 }
 
-export type Output = BaseOutput | FixedScriptWalletOutput;
+export type Output<TAmount = string | number> = BaseOutput<TAmount> | FixedScriptWalletOutput<TAmount>;
 
 export function isWalletOutput(output: Output): output is FixedScriptWalletOutput {
   return (
@@ -206,23 +206,36 @@ export interface ParseTransactionOptions<TNumber extends number | bigint = numbe
   reqId?: IRequestTracer;
 }
 
-export type ParsedTransaction<TNumber extends number | bigint = number> = {
+export type BaseParsedTransaction<TNumber extends number | bigint, TOutput> = {
   keychains: UtxoNamedKeychains;
   keySignatures: {
     backupPub?: string;
     bitgoPub?: string;
   };
-  outputs: Output[];
-  missingOutputs: Output[];
-  explicitExternalOutputs: Output[];
-  implicitExternalOutputs: Output[];
-  changeOutputs: Output[];
+  /** all transaction outputs */
+  outputs: TOutput[];
+  /** transaction outputs that were specified as recipients but are missing from the transaction */
+  missingOutputs: TOutput[];
+  /** transaction outputs that were specified as recipients and are present in the transaction */
+  explicitExternalOutputs: TOutput[];
+  /** transaction outputs that were not specified as recipients but are present in the transaction */
+  implicitExternalOutputs: TOutput[];
+  /** transaction outputs that are change outputs */
+  changeOutputs: TOutput[];
+  /** sum of all explicit external outputs */
   explicitExternalSpendAmount: TNumber;
+  /** sum of all implicit external outputs */
   implicitExternalSpendAmount: TNumber;
   needsCustomChangeKeySignatureVerification: boolean;
   customChange?: CustomChangeOptions;
 };
 
+/**
+ * This type is a bit silly because it allows the type for the aggregate amounts to be different from the type of
+ * individual amounts.
+ */
+export type ParsedTransaction<TNumber extends number | bigint = number> = BaseParsedTransaction<TNumber, Output>;
+
 export interface GenerateAddressOptions {
   addressType?: ScriptType2Of3;
   threshold?: number;