community[minor]: Fix long_context_reorder.py async (#22839)

Implement `async def atransform_documents( self, documents:
Sequence[Document], **kwargs: Any ) -> Sequence[Document]` for
`LongContextReorder`

libs/community/langchain_community/document_transformers/long_context_reorder.py

@@ -42,4 +42,4 @@ class LongContextReorder(BaseDocumentTransformer, BaseModel):
     async def atransform_documents(
         self, documents: Sequence[Document], **kwargs: Any
     ) -> Sequence[Document]:
-        raise NotImplementedError
+        return _litm_reordering(list(documents))