Function parse_ws_balance 

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

Parse a WebSocket account/balance message into a Balance.

OKX account update format:

{
  "arg": {"channel": "account"},
  "data": [{
    "uTime": "1700000000000",
    "totalEq": "100000.00",
    "details": [
      {"ccy": "USDT", "availBal": "50000", "frozenBal": "10000", "eq": "60000"},
      {"ccy": "BTC", "availBal": "1.5", "frozenBal": "0.5", "eq": "2.0"}
    ]
  }]
}