Warn if result backend is unset (#430)

* warn on .wait_result call if there is no result backend

* warn user on dummy result backend level

* use warn from warnings module

---------

Co-authored-by: Pavel Kirilin <win10@list.ru>

Author: igor-gorohovsky

taskiq/result_backends/dummy.py

@@ -1,3 +1,4 @@
+import warnings
 from typing import Any, TypeVar
 
 from taskiq.abc.result_backend import AsyncResultBackend
@@ -41,6 +42,11 @@ async def get_result(self, task_id: str, with_logs: bool = False) -> Any:
         :param with_logs: wether to fetch logs.
         :returns: TaskiqResult.
         """
+        warnings.warn(
+            "No result backend configured. Returning dummy result...",
+            stacklevel=2,
+        )
+
         return TaskiqResult(
             is_err=False,
             log=None,