feat: Add is_loop filter to library routes and update frontend API

Commit notes

This commit introduces an `is_loop` filter to the library routes, allowing users to query for looped or non-looped samples. The backend logic is updated to handle this new filter, enhancing the search functionality. Additionally, the frontend API is modified to include the `is_loop` property in the LibraryFilters interface, ensuring consistency across the application. This change improves the user experience by providing more refined search options in the library.