Incorrect Backorder Quantity Handling When Adding Same Product to Cart With Different Custom Options

[rutvik-monpara]

Fixed Issues

1. Fixes Incorrect Backorder Quantity Handling When Adding Same Product to Cart With Different Custom Options #3446: Incorrect Backorder Quantity Handling When Adding Same Product to Cart With Different Custom Options

Manual testing scenarios

1. Create a simple product with custom options.
2. Set product stock quantity to 10.

3. Enable backorders: Catalog > Products > Advanced Inventory > Backorders > Allow Qty Below 0 and Notify Customer
4. On frontend, add the same product to the cart twice, each with a different custom option. For each cart item, set quantity to 20.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)