feat: add expires_at to PurchaseDetailResponse and update checkout logic for pending payments

src/app/core/services/checkout.service.ts

@@ -61,6 +61,7 @@ export interface PurchaseDetailResponse extends PurchaseStatusResponse {
   user_id: number;
   created_at: string | null;
   payment_method: string | null;
+  expires_at: string | null;
   dni: string | null;
   transfer_payer_dni: string | null;
   telefono: string | null;