message: fix(utxo-lib): [psbt] reduce use of hackish `this.tx`
  Issue:
diff: @@ -147,7 +147,7 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  return new UtxoTransaction<bigint>(network);
  }
  - get tx(): Tx {
  + protected get tx(): Tx {
  return (this.data.globalMap.unsignedTx as PsbtTransaction).tx as Tx;
  }
  @@ -366,7 +366,6 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  hash: Buffer;
  sighashType: number;
  } {
  - const unsignedTx = this.tx;
  const sighashType = this.data.inputs[inputIndex].sighashType || Transaction.SIGHASH_DEFAULT;
  if (sighashTypes && sighashTypes.indexOf(sighashType) < 0) {
  throw new Error(
  @@ -374,6 +373,7 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  `sighashTypes array of whitelisted types. Sighash type: ${sighashType}`
  );
  }
  + const txInputs = this.txInputs; // These are somewhat costly to extract
  const prevoutScripts: Buffer[] = [];
  const prevoutValues: bigint[] = [];
  @@ -383,10 +383,10 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  // TODO: This could be costly, either cache it here, or find a way to share with super
  const nonWitnessUtxoTx = (this.constructor as typeof UtxoPsbt).transactionFromBuffer(
  input.nonWitnessUtxo,
  - unsignedTx.network
  + this.tx.network
  );
  - const prevoutHash = unsignedTx.ins[inputIndex].hash;
  + const prevoutHash = txInputs[inputIndex].hash;
  const utxoHash = nonWitnessUtxoTx.getHash();
  // If a non-witness UTXO is provided, its hash must match the hash specified in the prevout
  @@ -396,7 +396,7 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  );
  }
  - const prevoutIndex = unsignedTx.ins[inputIndex].index;
  + const prevoutIndex = txInputs[inputIndex].index;
  prevout = nonWitnessUtxoTx.outs[prevoutIndex];
  } else if (input.witnessUtxo) {
  prevout = input.witnessUtxo;
  @@ -406,7 +406,7 @@ export class UtxoPsbt<Tx extends UtxoTransaction<bigint>> extends Psbt {
  prevoutScripts.push(prevout.script);
  prevoutValues.push(prevout.value);
  }
  - const hash = unsignedTx.hashForWitnessV1(inputIndex, prevoutScripts, prevoutValues, sighashType, leafHash);
  + const hash = this.tx.hashForWitnessV1(inputIndex, prevoutScripts, prevoutValues, sighashType, leafHash);
  return { hash, sighashType };
  }
  }
  