addToCart method
Add item to cart.
Adds a product to the shopping cart with the specified quantity.
sku the product's SKU to add
quantity the quantity to add
productOption optional product options (size, color, etc.)
Returns true if item was added successfully, false otherwise.
Implementation
Future<bool> addToCart(
String sku,
int quantity, [
Map<String, dynamic>? productOption,
]) {
throw UnimplementedError('addToCart() has not been implemented.');
}