[FIX] Order Groups (prediction + perps)

[TexasCoding]

Scope

FIX Order Groups for both products — create/reset/delete/trigger group lifecycle.

Messages

• OrderGroupRequest (UOG), OrderGroupResponse (UOH).
• Tags: OrderGroupID (20130), OrderGroupAction (20131: CREATE/RESET/DELETE/TRIGGER_CANCEL/UPDATE), OrderGroupContractsLimit (20132), AllocAccount (79).

Work

• Typed order-group request/response models + helpers on the clients.
• Integrate OrderGroupID into the OE NewOrderSingle/OrderCancelReplaceRequest path.

Acceptance

Golden round-trip fixtures for UOG/UOH; lifecycle tests against the mock acceptor. ruff + mypy --strict clean.

Dependencies

Foundation #422; Order Entry. Part of #402.