feat: implement getFeaturedSongs method in SongService and add corresponding tests

- Added getFeaturedSongs method to SongService to retrieve featured songs across various timespans.
- Implemented tests for getFeaturedSongs to ensure correct functionality and handling of empty results.
- Removed SongBrowser module and related files as part of the refactor to streamline the service structure.
- Introduced new PageDto class for pagination handling in the database module.

Author: tomast1337