Add Binance SIM market adapter and exchange switch in settings.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/sim/matcher.py

@@ -40,7 +40,12 @@ class Matcher:
         return self.ledger.get_setting_float("fee_rate", get_settings().fee_rate)
 
     def _ct_mult(self, option_inst_id: str) -> float:
-        s = get_settings()
+        try:
+            from ..exchange.runtime import load_runtime_settings
+
+            s = load_runtime_settings()
+        except Exception:
+            s = get_settings()
         try:
             return get_exchange().get_ct_mult(
                 option_inst_id, s.option_inst_family, s.option_ct_mult_default
@@ -512,7 +517,7 @@ class Matcher:
         expiry_ms = None
         if expiry_ymd and len(expiry_ymd) == 6:
             try:
-                from ..exchange.okx.parse import expiry_ms_from_ymd
+                from ..exchange.expiry import expiry_ms_from_ymd
 
                 expiry_ms = expiry_ms_from_ymd(expiry_ymd)
             except Exception: