Add accepted leg edit notification and class leaderboard

lib/services/data_service/data_service_traction.dart

@@ -179,4 +179,39 @@ extension DataServiceTraction on DataService {
     }
     return null;
   }
+
+  Future<List<LeaderboardEntry>> fetchClassLeaderboard(
+    String locoClass, {
+    bool friends = false,
+  }) async {
+    try {
+      final path = Uri.encodeComponent(locoClass);
+      final suffix = friends ? '/friends' : '';
+      final json = await api.get('/stats/class/$path/leaderboard$suffix');
+      List<dynamic>? list;
+      if (json is List) {
+        list = json;
+      } else if (json is Map) {
+        for (final key in ['leaderboard', 'data', 'items', 'results']) {
+          final value = json[key];
+          if (value is List) {
+            list = value;
+            break;
+          }
+        }
+      }
+      return list
+              ?.whereType<Map>()
+              .map((e) => LeaderboardEntry.fromJson(
+                    e.map((k, v) => MapEntry(k.toString(), v)),
+                  ))
+              .toList() ??
+          const [];
+    } catch (e) {
+      debugPrint(
+        'Failed to fetch class leaderboard for $locoClass (friends=$friends): $e',
+      );
+      return const [];
+    }
+  }
 }