implemented absence report module with form validation, prefill support, and API integration

lib/api/marianumconnect/queries/absence/absence_prefill.dart

@@ -0,0 +1,10 @@
+import '../../marianumconnect_query.dart';
+import 'absence_prefill_response.dart';
+
+/// GETs the absence-report form prefill (`absence/prefill`, bearer-auth).
+class AbsencePrefill extends MarianumConnectQuery {
+  AbsencePrefill({super.dio});
+
+  Future<AbsencePrefillResponse> run() =>
+      getObject('absence/prefill', AbsencePrefillResponse.fromJson);
+}