Add is_trakt_group field to PlaylistGroup and update sorting logic

- Introduced `is_trakt_group` field in `PlaylistGroup` struct to differentiate between Trakt and non-Trakt groups.
- Updated relevant parsing functions in `m3u.rs`, `xtream.rs`, and `trakt.rs` to set this field appropriately.
- Enhanced sorting logic in `sort.rs` to prioritize Trakt groups during playlist sorting.
- Ensured backward compatibility by defaulting `is_trakt_group` to false where applicable.

backend/src/processing/processor/xtream_series.rs

@@ -197,6 +197,7 @@ async fn process_series_info(
                 title: plg.title.clone(),
                 channels: group_series,
                 xtream_cluster: XtreamCluster::Series,
+                is_trakt_group: false,
             });
         }
     }