fix: batchOrder json does not support booleans

Author: claudeenriquez

src/kraken/futures/trade.py

@@ -24,6 +24,7 @@
 
 from kraken.base_api import FuturesClient, defined
 
+import json
 
 class Trade(FuturesClient):
     """
@@ -239,7 +240,7 @@ def create_batch_order(
             }
         """
         batchorder: dict = {"batchOrder": batchorder_list}
-        params = {"json": f"{batchorder}"}
+        params = {"json": json.dumps(batchorder)}
         if processBefore:
             params["processBefore"] = processBefore