improved performance and battery usage on older devices

lib/state/app/modules/marianum_dates/data_provider/marianum_dates_get_events.dart

@@ -1,5 +1,6 @@
 import 'package:dio/dio.dart';
 import 'package:enough_icalendar/enough_icalendar.dart';
+import 'package:flutter/foundation.dart';
 
 import '../bloc/marianum_dates_state.dart';
 
@@ -19,6 +20,12 @@ class MarianumDatesGetEvents {
     final body = response.data;
     if (body == null || body.isEmpty) return [];
 
+    // The public feed holds hundreds of events back to 1981; parsing it on
+    // the UI isolate froze the page for a noticeable moment on every open.
+    return compute(parseEvents, body);
+  }
+
+  static List<MarianumDate> parseEvents(String body) {
     final root = VComponent.parse(body);
     final calendar = root is VCalendar ? root : null;
     final source = calendar?.children ?? root.children;