[Refactor] Improve type safety and pagination to GenreService

[Sethispr]

The current implementation of GenreService is decent using the service-client pattern and proper context handling. However, to ensure full API condition and improve developer experience, we should add some missing stuff.

1. Restore Pagination: The Anime/Manga endpoints support page and limit parameters. These should be added to the method signatures.

2. Introduce Type Safety for Filters: Instead of using raw strings literally just stringing everything so now for filter, we should implement a GenreFilter type with constants (GenresFilterThemes) to prevent runtime errors and improve IDE autocompletion.

// Current
func (s *GenreService) Anime(ctx context.Context, filter string) ([]Genre, error)

// New
func (s *GenreService) Anime(ctx context.Context, page, limit int, filter GenreFilter) ([]Genre, error)

The current version is clean enough, but adding it will make the library way better and user friendly for prod environments where pagination is needed.