Restrict event access and add extensive event tests

Updated event API to enforce stricter access controls based on user roles, including creators, managers, superusers, and guests. Added robust test cases for creating, fetching, and handling event access scenarios to ensure consistent behavior across endpoints.

backend/tests/conftest.py

@@ -78,6 +78,23 @@ def mock_user(db_session):
     db_session.commit()
     return mock_user
 
+@pytest.fixture
+def mock_superuser(db_session):
+    """Fixture to create and return a mock User instance."""
+    mock_user = User(
+        id=uuid.uuid4(),
+        email="mocksuperuser@example.com",
+        password_hash="mockhashedpassword",
+        first_name="Mock",
+        last_name="SuperUser",
+        phone_number="1234567890",
+        is_active=True,
+        is_superuser=True,
+        preferences=None,
+    )
+    db_session.add(mock_user)
+    db_session.commit()
+    return mock_user
 
 @pytest.fixture
 def mock_event(db_session, mock_user):