chore: remove dead code to eliminate all compiler warnings

- Remove unused get_artist() (replaced by get_artist_page())
- Remove unused Format::label(), Format::all()
- Remove unused QwsTokenResponse and QwsToken structs
- Remove unused PlayerCommand::Seek (seeking uses atomics directly)
- Remove unused PlayerState::Stopped, TrackInfo::format
- Remove unused PlayerStatus::get_current_track()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rust/src/lib.rs

@@ -410,7 +410,7 @@ pub unsafe extern "C" fn qobuz_backend_play_track(
         if let Some(dur) = track.duration {
             status.duration_secs.store(dur as u64, std::sync::atomic::Ordering::Relaxed);
         }
-        let _ = cmd_tx.send(player::PlayerCommand::Play(player::TrackInfo { track, url, format, replaygain_db }));
+        let _ = cmd_tx.send(player::PlayerCommand::Play(player::TrackInfo { track, url, replaygain_db }));
 
         // 5. State notification
         call_cb(cb, ud, EV_STATE_CHANGED, r#"{"state":"playing"}"#);