Function get_positions_by_task_submission_id 

pub async fn get_positions_by_task_submission_id(
    conn: &mut PgConnection,
    task_submission_id: Uuid,
) -> ModelResult<Vec<(Uuid, i32)>>

The files a submission recorded, paired with their positions, in stored order.

Reports the link rows as they stand; get_by_task_submission_ids instead joins file_uploads and so omits files whose upload row was deleted.