How can I override /packages/Webkul/Checkout/src/Cart.php and /packages/Webkul/Product/src/Type/AbstractType.php in my own package?
To override any facades, first of all, you need to create your own facades in your package extending with main facades (To whom you want to override).
Now in your facades, you can create method & can write your own logic.
You need to add the following line in your packages provider.
and can /packages/Webkul/Product/src/Type/AbstractType.php this class to your package.