Add highlights prop for cell highlighting (multi-user collaboration)

[nahooni0511]

Hello! I'm currently developing a real-time collaborative spreadsheet application using this library, where multiple users can actively edit the same sheet. In my use case, I need to display other users’ active cells on the grid. However, there was no existing functionality to highlight cells based on external states.

To address this, I've introduced a new highlights prop. This allows developers to pass in custom highlighting data—particularly useful for indicating which cells are active for other users. I’ve tried to follow the existing code style and methodology as closely as possible for consistency.

Additionally, I’ve updated the Storybook examples to simulate real-time highlighting behavior, making it easy to see how the feature works in practice.

Thank you for reviewing this! I’m happy to discuss any feedback or make adjustments as needed.