Freebie item affects product kit discount calculation

[vitorrgg]

Bug description

When a cart has an active freebie rule (e.g. a gift product added via coupon) alongside a product_kit_discounts rule that uses discount_lowest_price: true and check_all_items: true, the freebie item is incorrectly included in the kit discount calculation in two ways:

1. Price: because the freebie has a lower price than the regular products, it becomes the "lowest price" used as the discount base value, drastically reducing the kit discount.
2. Quantity: the freebie item is counted towards the minimum quantity required to trigger the kit rule, which can incorrectly activate the discount.

Steps to reproduce

1. Configure a product_kit_discounts rule with min_quantity: 5, check_all_items: true, discount_lowest_price: true (leve X pague Y style).
2. Configure a freebies_rules entry with a freebie_coupon pointing to a product cheaper than the regular cart items.
3. Add 5+ regular items to the cart and apply the freebie coupon.
4. The extra_discount value will be computed using the freebie's price instead of the regular items' price.

Expected behavior

Freebie products should be excluded from product_kit_discounts calculations entirely — neither their price nor their quantity should influence the kit rule.

Actual behavior

With 11 regular items (R$15.90 each) + 1 freebie (R$6.90):

	Without fix	Expected
Lowest price used	R$6.90 (freebie)	R$15.90
Kit discount (2 kits)	R$13.80	R$31.80
Freebie discount	R$6.90	R$6.90
Total	R$20.70	R$38.70