fix:discount coupon code not reflected if added in payment step

[AAbbadi]

Problem
When a customer applies or removes a discount code during the Payment step of the checkout flow, the Checkout.com payment request does not reflect the updated order total.

This occurs because the payment object/payload is initialized when the user first lands on the payment step. Since applying a coupon in Magento's standard checkout doesn't always trigger a full re-initialization of the payment component's internal data, the extension continues to pass the original amount (pre-discount) to the Checkout.com API. This results in the customer being charged the full price despite a coupon being successfully applied to the Magento quote.

Solution
I have updated the logic to ensure that the payment totals are recalculated/refreshed whenever the quote's "totals" object is updated. This ensures that the final payload sent to Checkout.com always contains the most recent grand_total including any discounts applied at the last minute.

Changes

1. Added a subscriber/trigger to watch for totals changes during the payment step.
2. Forced a refresh of the payment amount calculation before the transaction is initialized.

How to Test

1. Add products to the cart and proceed to Checkout.
2. Navigate to the Payment step without applying a coupon first.
3. Observe the "Order Summary" total.
4. Apply a valid discount code in the "Apply Discount Code" section.
5. Verify that the Checkout.com payment request now uses the discounted amount instead of the original amount.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud