pub async fn get_by_exercise_task_submission_id(
    conn: &mut PgConnection,
    exercise_task_submission_id: Uuid,
) -> ModelResult<Option<ExerciseTaskGrading>>pub async fn get_by_exercise_task_submission_id(
    conn: &mut PgConnection,
    exercise_task_submission_id: Uuid,
) -> ModelResult<Option<ExerciseTaskGrading>>