Add a 'hide duplicates' option

I know #14 was about adding the ability to sort by color in order to find duplicates, which is very handy, but I have a project that has duplicates _on purpose_ (i.e., setting a less variable like `@error-color` to another less variable like `@red`). It'd be nice to be able to toggle duplicates on and off, to get an overview of the unique colors in the project.

What do you think?

This is a very useful package, thanks!

Look at the code that currently finds and lists colors, likely in the main package file. Understand how duplicates are currently identified and displayed. The feature requires adding a UI toggle to filter duplicates, which involves modifying the view logic and possibly the color aggregation logic. Check for existing settings or toggle patterns in the codebase.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.