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/parser/m3u.rs

@@ -266,7 +266,7 @@ where
         if let Some((cluster, group_title)) = channel.map(|pli|
             (pli.header.xtream_cluster, &pli.header.group)) {
             grp_id += 1;
-            Some(PlaylistGroup { id: grp_id, xtream_cluster: cluster, title: group_title.to_string(), channels })
+            Some(PlaylistGroup { id: grp_id, xtream_cluster: cluster, title: group_title.to_string(), channels, is_trakt_group: false })
         } else {
             None
         }