feat(payments): improve VNPay, MoMo, ZaloPay services with ConfigService

Migrate payment gateway services from hardcoded config to NestJS
ConfigService injection. Improve payment handler error handling and
update gateway factory specs.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/payments/infrastructure/services/vnpay.service.ts

@@ -1,6 +1,6 @@
 import * as crypto from 'crypto';
 import { Injectable, Logger } from '@nestjs/common';
-import { ConfigService } from '@nestjs/config';
+import { type ConfigService } from '@nestjs/config';
 import { type PaymentProvider } from '@prisma/client';
 import {
   type IPaymentGateway,