Subscribe to Order book updates: Request snapshot data.

[serj20]

Please add op: "request" for BitMartSocketOperation

When subscribing to order book updates (SubscribeToOrderBookUpdatesAsync), data reloading is not possible if the version sequence is broken.

Here's the documentation on how it works:

https://developer-pro.bitmart.com/en/spot/#public-depth-increase-channel

7. Request through request {"op": "request", "args": ["spot/depth/increase100:<symbol>"] }to obtain the latest depth snapshot (type=snapshot in the message), and add the depth The content in the snapshot is overwritten to the local cache, and then the logic continues from step 2.