code: public Map<DeckReference, AlbumArt> getLoadedArt() {
          ensureRunning();
          // Make a copy so callers get an immutable snapshot of the current state.
          return Collections.unmodifiableMap(new HashMap<DeckReference, AlbumArt>(hotCache));
      }
docs: Get the art available for all tracks currently loaded in any player, either on the play deck, or in a hot cue.
  
  @return the album art associated with all current players, including for any tracks loaded in their hot cue slots
  
  @throws IllegalStateException if the ArtFinder is not running