Feature: add states filter to SearchLimitOrdersRequest (#172)

Add optional states field to SearchLimitOrdersRequest allowing clients to
filter limit orders by their state when searching. This enables more targeted
queries for specific order states (e.g., pending, filled, cancelled).

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: BRBussy

go/trading/limit_order/v1/service.pb.go

@@ -252,11 +252,16 @@ message SearchLimitOrdersRequest {
     string: {pattern: "^accounts/[0123456789ABCDEFGHJKMNPQRSTVWXYZ]{26}$"}
   }];
 
+  /*
+     Filter by states (optional).
+  */
+  repeated LimitOrderState states = 3;
+
   /*
      When true, fetches live ledger data for matching orders.
      When false, returns only stored metadata.
   */
-  bool live_ledger_data = 3;
+  bool live_ledger_data = 4;
 }
 
 /*