Cleanup order events

Author: cjdsellers

nautilus_core/model/src/events/order/cancel_rejected.rs

@@ -282,7 +282,7 @@ impl OrderEvent for OrderCancelRejected {
     }
 
     fn commission(&self) -> Option<Money> {
-        todo!()
+        None
     }
 
     fn ts_event(&self) -> UnixNanos {

nautilus_core/model/src/events/order/canceled.rs

@@ -152,7 +152,7 @@ impl OrderEvent for OrderCanceled {
     }
 
     fn currency(&self) -> Option<Currency> {
-        todo!()
+        None
     }
 
     fn client_order_id(&self) -> ClientOrderId {

nautilus_core/model/src/events/order/released.rs

@@ -161,7 +161,7 @@ impl OrderEvent for OrderReleased {
     }
 
     fn liquidity_side(&self) -> Option<LiquiditySide> {
-        todo!()
+        None
     }
 
     fn post_only(&self) -> Option<bool> {