Implement faster pagination for library

[anultravioletaurora]

This pull request adds support for efficient A-Z (letter) navigation in paginated lists of artists, albums, and tracks by introducing a "letter cursor" mechanism to each entity's React Query hook. This allows the A-Z scroller component to jump directly to the page containing a tapped letter, rather than paginating through every page sequentially. The implementation includes new utility functions to quickly count the number of items before a given letter, updated hook return values, and thorough documentation of the pattern.

The most important changes are:

A-Z Scroller Integration for Infinite Lists:

• Added a letterCursor object to the return value of useInfiniteQuery hooks for artists, albums, and tracks (useAlbumArtists, useAlbums, useTracks, and useArtistTracks). This object provides methods to fetch a specific page and to count items before a given letter, enabling instant jumps in the A-Z scroller. [1] [2] [3] [4]

New Utility Functions for Counting Items Before a Letter:

• Implemented fetchArtistsCountBeforeLetter, fetchAlbumsCountBeforeLetter, and fetchTracksCountBeforeLetter utility functions. These use the Jellyfin API with the nameLessThan and enableTotalRecordCount options to efficiently determine how many items precede a given letter, avoiding unnecessary pagination. [1] [2] [3]

Query Hook Refactoring:

• Refactored query hooks to extract and reuse queryKey arrays, facilitating their use in the new letterCursor objects and improving code clarity. [1] [2] [3] [4]

Documentation:

• Added a comprehensive README (src/api/queries/README.md) describing the folder structure, infinite query design, and the new letter cursor mechanism, including usage details and rationale.

Type and Import Updates:

• Updated imports and type definitions to include the new LetterCursor type and utility functions where needed in the query hooks. [1] [2] [3]

These changes collectively improve the user experience for navigating large music libraries by making A-Z jumps instantaneous and memory-efficient.