feature(training): Добавлен состояния загрузки, пустоты и наличие данных на экране тренировки

lib/screens/training/cubit/training_state.dart

@@ -0,0 +1,9 @@
+part of 'training_cubit.dart';
+
+@freezed
+class TrainingState with _$TrainingState {
+  const factory TrainingState.loading() = _Loading;
+  const factory TrainingState.empty() = _Empty;
+  const factory TrainingState.data() = _Data;
+  const factory TrainingState.result() = _Result;
+}