feat(catalog): implement maximum addable quantity logic and user quota sharing across variants

app/Domains/Purchase/Services/Checkout/StartCheckoutService.php

@@ -243,7 +243,7 @@ class StartCheckoutService
 
         $this->loadCartItems($cartItems);
         $this->verifyTenantItems($tenant, $cartItems);
-        $this->assertCartPurchaseLimits($tenant, $userId, $cartItems);
+        $this->assertCartPurchaseLimits($tenant, $userId, $cartItems, $cart->getKey());
         $cart->setRelation('items', $cartItems);
 
         $purchase = $this->createPurchase(
@@ -312,6 +312,7 @@ class StartCheckoutService
         Tenant $tenant,
         int $userId,
         Collection $cartItems,
+        int $cartId,
     ): void {
         $quantities = $cartItems
             ->groupBy('catalog_item_id')
@@ -333,6 +334,7 @@ class StartCheckoutService
                 $catalogItem,
                 $userId,
                 $quantity,
+                excludedCartId: $cartId,
                 field: 'cart_id',
             );
         }