fix(core-flows, link-module): product <> inventory delete cascades (#9528)

**What**
- remove cascade delete of inventory items on product delete
- implement inventory deletion in product/variant delete workflows with checks:
  - product/variant cannot be deleted if there are reservations associated with their inventory items
  - inventory item will be cascade deleted if it's not used by other variants (that are not being deleted in the current flow)

---

FIXES CC-581 CC-582

packages/modules/link-modules/src/definitions/product-variant-inventory-item.ts

@@ -44,7 +44,6 @@ export const ProductVariantInventoryItem: ModuleJoinerConfig = {
       args: {
         methodSuffix: "InventoryItems",
       },
-      deleteCascade: true,
     },
   ],
   extends: [