`valueClassName` support to `renderDummyList` for enhanced styling flexibility

[daeseong9388]

I'm currently trying to implement a text gradient effect using background-clip: text. However, this effect needs to be applied within the container of the text itself.

https://github.com/almond-bongbong/react-slot-counter/blob/0e21537c4f74968686d6fe5347e02572cc1aa313/src/components/Slot.tsx#L147C6-L158C14

I would like to request the enhancement of the renderDummyList function to accept an additional className prop. This would allow for individual styling of the dummy list items, similar to how valueClassName is used for the main value elements.

Thank you for considering this feature request. I appreciate the work that has been put into the this project and am looking forward to possibly contributing to its further development with this enhancement.