Function parse_ws_balance 

pub fn parse_ws_balance(msg: &Value) -> Result<Balance>

Parse a WebSocket account/balance message into a Balance.

Bitget account update format:

{
  "arg": {"instType": "SPOT", "channel": "account", "coin": "default"},
  "data": [{
    "coin": "USDT",
    "available": "50000",
    "frozen": "10000",
    "uTime": "1700000000000"
  }]
}