improve stats handling

anatomy/migrations/0005_exam_stats_graph.py

@@ -0,0 +1,18 @@
+# Generated by Django 4.1.4 on 2024-01-08 22:16
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('anatomy', '0004_exam_candidates_only_alter_exam_active_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='exam',
+            name='stats_graph',
+            field=models.TextField(default=0),
+        ),
+    ]