Coinex/Phemex-style subscribe frame where the method name IS the channel.
%{"method" => "ticker.subscribe", "params" => [], "id" => 1}Callers pass full method names like ["ticker.subscribe"] in the
channel list. Only the first entry is used — callers that need multiple
subscriptions call subscribe/2 once per channel. unsubscribe/2
converts .subscribe suffixes to .unsubscribe.
Config keys: :op_field (default "method"), :args_field
(default "params").
Not wired in CCXT.WS.Config today (no priority-tier exchange uses it).