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>)>