🚨(backend) fix linter warnings

Recent updates of dev/ruff and dev/pylint dependencies led
to new linting warnings.

Pylint 3.2.0 introduced a new check `possibly-used-before-assignment`,
which ensures variables are defined regardless of conditional statements.

Some if/else branches were missing defaults. These have been fixed.

src/backend/core/utils.py

@@ -1,6 +1,7 @@
 """
 Utils functions used in the core app
 """
+
 from typing import Optional
 from uuid import uuid4