timetable performance optimization

lib/state/app/modules/foreign_timetable/bloc/foreign_timetable_bloc.dart

@@ -45,7 +45,7 @@ class ForeignTimetableBloc
   TimetableState fromNothing() {
     final reference = DateTime.now().addDays(2);
     return TimetableState(
-      startDate: _startOfWeek(reference),
+      startDate: reference.mondayOfWeek,
       endDate: _endOfWeek(reference),
     );
   }
@@ -101,7 +101,7 @@ class ForeignTimetableBloc
 
   void resetWeek() {
     final reference = DateTime.now().addDays(2);
-    changeWeek(_startOfWeek(reference), _endOfWeek(reference));
+    changeWeek(reference.mondayOfWeek, _endOfWeek(reference));
   }
 
   void refresh() => fetch();
@@ -180,19 +180,7 @@ class ForeignTimetableBloc
   }
 
   void _writeWeekToCache(DateTime weekStart, TimetableGetWeekResponse week) {
-    final key = weekStart.weekKey();
-    add(
-      Emit((s) {
-        final updated = Map<String, TimetableGetWeekResponse>.of(s.weekCache);
-        updated[key] = week;
-        return s.copyWith(weekCache: updated, dataVersion: s.dataVersion + 1);
-      }),
-    );
-  }
-
-  static DateTime _startOfWeek(DateTime reference) {
-    final monday = reference.subtractDays(reference.weekday - 1);
-    return DateTime(monday.year, monday.month, monday.day);
+    add(Emit((s) => s.withFetchedWeek(weekStart, week)));
   }
 
   static DateTime _endOfWeek(DateTime reference) {