feat: Implement sharing functionality for CidUserExam attempts, including user management and sharing settings

Co-authored-by: Copilot <copilot@github.com>

generic/migrations/0032_ciduserexam_shared_with_users.py

@@ -0,0 +1,23 @@
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("generic", "0031_flag"),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="ciduserexam",
+            name="shared_with_users",
+            field=models.ManyToManyField(
+                blank=True,
+                help_text="Users with whom this attempt has been manually shared.",
+                related_name="shared_cid_user_exams",
+                to=settings.AUTH_USER_MODEL,
+            ),
+        ),
+    ]