malkhut(wire): OrderType as three orthogonal dimensions — Fable's corrections

CRITICAL REFACTOR based on Fable's review (S9 roadmap item):

Before: flat enum conflating order types with TIF/instructions
  OrderType had MARKET, LIMIT, IOC, FOK, POST_ONLY, REDUCE_ONLY, etc.

After: three orthogonal dimensions (FIX-aligned):
  1. OrderType (Tag 40): what the order IS
     LIMIT, MARKET, STOP_MARKET, STOP_LIMIT, TRIGGER_MARKET, TRIGGER_LIMIT,
     TRAILING_STOP, OCO, TP_SL
  2. TimeInForce (Tag 59): how long it LIVES
     GTC, IOC, FOK, GTD
  3. Instructions (Tag 18): behavioral modifiers
     POST_ONLY, REDUCE_ONLY, HIDDEN, ICEBERG

Key corrections:
- POST_ONLY is an instruction on a LIMIT order, not a standalone type
- IOC/FOK are TimeInForce values, not order types
- BingX trailing_stop -> native TRAILING_STOP_MARKET (not TRIGGER_MARKET)
- FulfilmentAction.time_in_force: new field, default GTC

Exchange mappings restructured:
  EXCHANGE_ORDER_TYPE_MAP: OrderType -> exchange native 'type' param
  EXCHANGE_TIF_MAP: TimeInForce -> exchange native 'timeInForce' param
  EXCHANGE_INSTRUCTION_MAP: Instruction -> exchange encoding

21 files changed. 380+ tests pass. Backward compatible.

MALKHUT/malkhut/tests/test_adversarial.py

@@ -132,7 +132,7 @@ class TestRiskGateAdversarial:
         gate = RiskGate()
         state = _state_with_intent()
         action = FulfilmentAction(
-            ActionKind.PLACE, Side.BUY, OrderType.POST_ONLY, -10, 0.1, 200, post_only=True,
+            ActionKind.PLACE, Side.BUY, OrderType.LIMIT, -10, 0.1, 200, post_only=True,
         )
         planned = PlannedPolicy(actions=(action,), probabilities=(1.0,),
                                 selected_action=action, diagnostics={})