List quiz question-bank assignments

Response envelope for GET /v2/quizzes/{quiz_id}/question-banks/.

A plain, non-paginated {"data": [...]} list: a quiz's bank assignments are a small bounded set, so — unlike the quizzes/question-banks/questions read lists — this endpoint does NOT use CursorPaginator and carries no meta / links / next_cursor pagination fields. Ordering follows the model's Meta.ordering (order, then created_at).