improved performance and battery usage on older devices

lib/widget_data/widget_data_mapper.dart

@@ -1,7 +1,5 @@
 import 'dart:developer';
 
-import 'package:rrule/rrule.dart';
-
 import '../api/marianumconnect/queries/timetable_get_holidays/timetable_get_holidays_response.dart';
 import '../api/marianumconnect/queries/timetable_get_rooms/timetable_get_rooms_response.dart';
 import '../api/marianumconnect/queries/timetable_get_subjects/timetable_get_subjects_response.dart';
@@ -10,6 +8,7 @@ import '../api/marianumconnect/queries/timetable_get_week/timetable_get_week_res
 import '../api/mhsl/custom_timetable_event/custom_timetable_event.dart';
 import '../api/mhsl/custom_timetable_event/get/get_custom_timetable_event_response.dart';
 import '../extensions/date_time.dart';
+import '../utils/recurrence_occurrences.dart';
 import '../view/pages/timetable/data/lesson_labels.dart';
 import '../view/pages/timetable/data/lesson_merger.dart';
 import '../view/pages/timetable/data/lesson_period_schedule.dart';
@@ -443,11 +442,13 @@ class WidgetDataMapper {
     }
 
     try {
-      final parsed = RecurrenceRule.fromString(rule);
       final anchorUtc = event.startDate.toUtc();
-      for (final occUtc in parsed.getInstances(start: anchorUtc)) {
-        if (!occUtc.isBefore(rangeEndUtc)) break;
-        if (occUtc.isBefore(rangeStartUtc)) continue;
+      for (final occUtc in RecurrenceOccurrences.between(
+        rule,
+        anchorUtc,
+        rangeStartUtc,
+        rangeEndUtc,
+      )) {
         final occLocal = occUtc.toLocal();
         final occStart = DateTime(
           occLocal.year,