OKX-style subscribe frame with object-valued args.
%{
"op" => "subscribe",
"args" => [
%{"channel" => "tickers", "instId" => "BTC-USDT"},
%{"channel" => "books", "instId" => "BTC-USDT"}
]
}Callers pass pre-built channel objects (maps). Same frame shape as
OpSubscribe; the difference is that args contains maps instead of
strings. Config keys: :op_field (default "op"), :args_field
(default "args").