Flesh out order management on the Trading API client

Flesh out order management on the Trading API client: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). Right now TradingClient can only submit a new order ( submit order ). That's not enough to actually manage orders against the Alpaca trading API — there's no way…