By name: add-cart-discount description: Add per-item discount support to the cart total
Add per-item discounts
total(items) in src/cart.js sums price * qty across the cart.
Add support for an optional discount field on an item — a percentage off
that item's line total. For example an item { price: 100, qty: 1, discount: 10 }
contributes 90. Items without a discount field are unaffected.
The behaviour is covered by the tests under test/.