Added functionality to retrieve and parse the home page content in YTMusic class. The `getHome` method fetches home page data and uses the new `Parser.parseMixedContent` method to parse the content into `HomePageContent` type. Also, updated AlbumParser to handle potential null values more gracefully and added PlaylistWatch type parsing.
- Added `FE_MUSIC_HOME` constant for home page ID.
- Implemented `getHome` method in `YTMusic` class.
- Created `parseMixedContent` in `Parser` class.
- Updated `AlbumParser` and `SongParser` to handle nullable fields.
- Added `PlaylistWatch` type and parsing in `PlaylistParser`.
- Added tests for the new home page content feature.