Add event firing for carousel index updates

[iqbl-nrkhls]

This PR introduces event firing for carousel index updates, allowing developers to track changes when the user navigates through slides. This improves reactivity and integration with other UI components.

Changes:

• Implemented event dispatching on index change

Why This is Needed:
Currently, there is no built-in way to detect slide changes in the carousel. With this feature, developers can listen for index updates and trigger custom actions, animations, or syncing external components.

How to use:

const instance = HSCarousel.getInstance("#carousel");

instance.on("update", (currentIndex) => {
  console.log(currentIndex);
});