Fix Dataset.iterate_items

Fix typing issue.
Abstract AsyncIterator can't be defined with async and missing yield.
https://stackoverflow.com/questions/68905848/how-to-correctly-specify-type-hints-with-asyncgenerator-and-asynccontextmanager

Author: Pijukatel

src/crawlee/base_storage_client/_base_dataset_client.py

@@ -87,7 +87,7 @@ async def list_items(
         """
 
     @abstractmethod
-    async def iterate_items(
+    def iterate_items(
         self,
         *,
         offset: int = 0,

src/crawlee/memory_storage_client/_dataset_client.py

@@ -203,7 +203,7 @@ async def list_items(
             )
 
     @override
-    async def iterate_items(  # type: ignore
+    async def iterate_items(
         self,
         *,
         offset: int = 0,

src/crawlee/storages/_dataset.py

@@ -404,7 +404,7 @@ async def iterate_items(
         Yields:
             Each item from the dataset as a dictionary.
         """
-        async for item in self._resource_client.iterate_items(  # type: ignore
+        async for item in self._resource_client.iterate_items(
             offset=offset,
             limit=limit,
             clean=clean,