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/domain/value-objects/money.vo.ts

@@ -1,5 +1,4 @@
-import { Result } from '@modules/shared/domain/result';
-import { ValueObject } from '@modules/shared/domain/value-object';
+import { Result, ValueObject } from '@modules/shared';
 
 interface MoneyProps {
   amountVND: bigint;