feat(checkout) PI-5213 Affirm orderSubmit only after payment complete

[bc-dronov]

What/Why?

Affirm Order Submitting only after payment is complete.

Rollout/Rollback

Revert PR, OR experiment disable.

Testing

Manual testing

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Note

Medium Risk
Changes the order submission timing in the Affirm payment flow and switches data sources for the Affirm checkout payload, which could affect totals/discounts and sequencing around payment authorization.

Overview
Affirm checkout can now postpone order creation. AffirmPaymentStrategy.execute reads initializationData.postponeOrderCreation and conditionally calls submitOrder before or after the Affirm modal succeeds, while still submitting the payment nonce afterwards.

Affirm payload generation now uses cart/checkout data instead of order data. getCheckoutInformation pulls totals and order_id from checkout, and items/discounts from cart (lineItems, coupons, discountAmount), with tests updated to cover both sequencing modes and expanded item expectations.

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