Add __str__ method to QueueSendResult

This commit introduces

Author: liornabat-sealights

kubemq/queues/queues_send_result.py

@@ -62,3 +62,8 @@ def decode(cls, result: SendQueueMessageResult) -> "QueueSendResult":
 
     class Config:
         arbitrary_types_allowed = True
+    def __str__(self):
+        return (
+            f"QueueSendResult: id={self.id}, sent_at={self.sent_at}, expired_at={self.expired_at}, "
+            f"delayed_to={self.delayed_to}, is_error={self.is_error}, error={self.error}"
+        )