improved performance and battery usage on older devices

lib/api/marianumconnect/queries/timetable_custom_events/custom_events_migration.dart

@@ -1,6 +1,6 @@
 import 'dart:developer';
 
-import 'package:localstore/localstore.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 import '../../../../model/account_data.dart';
 import '../../../demo/demo_mode.dart';
@@ -21,9 +21,7 @@ import 'timetable_custom_events_add.dart';
 /// failure only sees the events that were not yet moved, so nothing is
 /// duplicated. The flag is set only once MHSL reports no remaining events.
 class CustomEventsMigration {
-  static const String _collection = 'MarianumMobile';
-  static const String _document = 'customEventsMigration';
-  static const String _doneKey = 'migratedToMc';
+  static const String _doneKey = 'customEventsMigratedToMc';
 
   const CustomEventsMigration._();
 
@@ -57,17 +55,11 @@ class CustomEventsMigration {
     }
   }
 
-  static Future<bool> _isDone() async {
-    final data = await Localstore.instance
-        .collection(_collection)
-        .doc(_document)
-        .get();
-    return data != null && data[_doneKey] == true;
-  }
+  // SharedPreferences, like the old cache document, is cleared on sign-out,
+  // so the next account runs its own migration.
+  static Future<bool> _isDone() async =>
+      (await SharedPreferences.getInstance()).getBool(_doneKey) ?? false;
 
-  static Future<void> _markDone() async {
-    await Localstore.instance.collection(_collection).doc(_document).set({
-      _doneKey: true,
-    });
-  }
+  static Future<void> _markDone() async =>
+      (await SharedPreferences.getInstance()).setBool(_doneKey, true);
 }

lib/api/marianumconnect/queries/timetable_get_week/timetable_get_week_response.dart

@@ -76,10 +76,17 @@ class McTimetableEntry {
 
   /// Combines the calendar date with the hour/minute portion of [startTime]
   /// (which carries a 1970 placeholder date) into a real DateTime.
-  DateTime get startDateTime =>
+  DateTime get startDateTime => _startDateTime;
+
+  DateTime get endDateTime => _endDateTime;
+
+  // Cached (private, so json_serializable ignores them): sorting and lesson
+  // merging read these per comparison, and every local DateTime construction
+  // does a timezone lookup.
+  late final DateTime _startDateTime =
       DateTime(date.year, date.month, date.day, startTime.hour, startTime.minute);
 
-  DateTime get endDateTime =>
+  late final DateTime _endDateTime =
       DateTime(date.year, date.month, date.day, endTime.hour, endTime.minute);
 
   static DateTime _dateFromJson(String raw) => DateTime.parse(raw);