Fix SKU retrieval logic for order items

[dgoemans]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes the SKU retrieval logic for order items to prioritize variant SKUs when available. The change ensures that when a product has variants, the system returns the specific variant's SKU rather than the parent product's SKU.

• Updates SKU retrieval to check for variant SKU first before falling back to product SKU

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