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/trakt.rs

@@ -206,6 +206,7 @@ fn create_category_from_matches<'a>(
         title: String::from(group_title),
         channels: matched_items,
         xtream_cluster: cluster,
+        is_trakt_group: true,
     })
 }