feat: Implement group management with BLoC pattern; add GroupBloc, GroupRepository, and related models

NOT FUNCTIONNAL

lib/blocs/group/group_state.dart

@@ -8,33 +8,38 @@ abstract class GroupState extends Equatable {
   List<Object?> get props => [];
 }
 
+// État initial
 class GroupInitial extends GroupState {}
 
+// Chargement
 class GroupLoading extends GroupState {}
 
-class GroupLoaded extends GroupState {
+// Groupes chargés
+class GroupsLoaded extends GroupState {
   final List<Group> groups;
 
-  const GroupLoaded({required this.groups});
+  const GroupsLoaded(this.groups);
 
   @override
   List<Object?> get props => [groups];
 }
 
+// Succès d'une opération
 class GroupOperationSuccess extends GroupState {
   final String message;
 
-  const GroupOperationSuccess({required this.message});
+  const GroupOperationSuccess(this.message);
 
   @override
   List<Object?> get props => [message];
 }
 
+// Erreur
 class GroupError extends GroupState {
   final String message;
 
-  const GroupError({required this.message});
+  const GroupError(this.message);
 
   @override
   List<Object?> get props => [message];
-}
+}