[Enhancement]: Implement COGS

### Describe the solution you'd like

WooCommerce is going to add COGS into Core.
See [Blog](https://developer.woocommerce.com/2025/05/21/cost-of-goods-soldcogs-is-ready-to-blossom-out-of-beta-this-summer/)

We should add COGS to Smooth-Generator :)
Price should always be lower to Regular price

### Describe alternatives you've considered

_No response_

### Additional context

_No response_