Function headless_lms_models::exercises::get_or_select_exercise_slide

pub async fn get_or_select_exercise_slide(
    conn: &mut PgConnection,
    user_id: Option<Uuid>,
    exercise: &Exercise,
    fetch_service_info: impl Fn(Url) -> BoxFuture<'static, ModelResult<ExerciseServiceInfoApi>>
) -> ModelResult<(CourseMaterialExerciseSlide, Option<CourseInstanceOrExamId>)>