Fix code review issues - correct random range and improve comments
- Change print_song_info() range from 0..5 to 0..6 to make case 5 reachable
- Add detailed comments explaining why all fields are needed in API structs
- Re-add #[allow(dead_code)] with explanation for deserialization requirements
Co-authored-by: jchoi2x <2028917+jchoi2x@users.noreply.github.com>