feat: refactor cart and bundle handling to support Buyable interface for improved flexibility

app/Domains/Shared/Contracts/Buyable.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Domains\Shared\Contracts;
+
+interface Buyable
+{
+    public function getPrice(): float;
+
+    public function getName(): string;
+
+    public function availableQuantity(): ?int;
+
+    public function reserveStock(int $amount): void;
+
+    public function decrementReservedStock(int $amount): void;
+
+    public function buy(int $amount): void;
+
+    public function validateStock(): void;
+}