fix: correct NAT question parsing and cache custom exam courses

packages/core/lib/data/models/question_dto.dart

@@ -133,6 +133,14 @@ class QuestionDto {
         'S' => 'shortAnswer',
         'N' => 'numerical',
         'E' => 'essay',
+        final String t when t.contains('Numerical') || t.contains('NAT') =>
+          'numerical',
+        final String t
+            when t.contains('Multiple Choice') || t.contains('MCQ') =>
+          'singleSelect',
+        final String t
+            when t.contains('Multiple Select') || t.contains('MSQ') =>
+          'multipleSelect',
         _ => 'singleSelect',
       },
       subject:

packages/core/test/data/models/question_dto_test.dart

@@ -23,6 +23,26 @@ void main() {
         );
       },
     );
+
+    test('parses verbose string types correctly', () {
+      final natQuestion = QuestionDto.fromJson({
+        'id': '1',
+        'type': 'NAT, Numerical Answer Type',
+      });
+      expect(natQuestion.type, 'numerical');
+
+      final mcqQuestion = QuestionDto.fromJson({
+        'id': '2',
+        'type': 'MCQ, Multiple Choice Type',
+      });
+      expect(mcqQuestion.type, 'singleSelect');
+
+      final msqQuestion = QuestionDto.fromJson({
+        'id': '3',
+        'type': 'MSQ, Multiple Select Type',
+      });
+      expect(msqQuestion.type, 'multipleSelect');
+    });
   });
 
   group('AnswerDto', () {

packages/exams/lib/providers/custom_exam_courses_provider.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'package:core/data/data.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 import '../repositories/custom_exam_repository.dart';
@@ -8,6 +9,12 @@ part 'custom_exam_courses_provider.g.dart';
 class CustomExamCourses extends _$CustomExamCourses {
   @override
   FutureOr<List<CourseDto>> build() async {
+    final link = ref.keepAlive();
+    final timer = Timer(const Duration(minutes: 5), () {
+      link.close();
+    });
+    ref.onDispose(() => timer.cancel());
+
     final repository = ref.watch(customExamRepositoryProvider);
 
     // Fetch courses with allow_custom_test=true