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## Market data

* Added `GET /api/v5/market/history-mark-price-candles` for historical mark
  price candlesticks, complementing the existing index and trade-price candle
  endpoints.
* The order book endpoint `GET /api/v5/market/books` now accepts a `sz` value
  up to `400` for spot and margin instruments (previously `400` was restricted
  to specific instrument types).
* New WebSocket channel `mark-price-candle{bar}` delivers mark price candles in
  real time, matching the request-cadence of `index-candle{bar}`.