doc(reducer): fix imports+indentation for function-based reducer

Signed-off-by: Martin Thøgersen <martint@martint.dk>

Author: th0ger

examples/reduce/README.md

@@ -33,7 +33,7 @@ For creating a reducer UDF we can use two different approaches:
       # We are passing the init_args for the class instance.
       grpc_server = ReduceAsyncServer(Example, init_args=(0,))
       grpc_server.start()
-  ``` 
+  ```
 
 - Function based reducer
     For the function based reducer we need to create a function of the signature
@@ -45,23 +45,23 @@ For creating a reducer UDF we can use two different approaches:
     - Finally we need to call the `start` method on the `ReduceAsyncServer` instance to start the reducer server.
     - We must ensure that no init_args or init_kwargs are passed to the `ReduceAsyncServer` instance as they are not used for function based reducers.
     ```python
-        from numaflow import ReduceAsyncServer
-        async def handler(keys: list[str], datums: AsyncIterable[Datum], md: Metadata) -> Messages:
-            counter = 0
-            interval_window = md.interval_window
-            async for _ in datums:
-                counter += 1
-            msg = (
-                f"counter:{counter} interval_window_start:{interval_window.start} "
-                f"interval_window_end:{interval_window.end}"
-            )
-            return Messages(Message(str.encode(msg), keys=keys))
-    
-        if __name__ == "__main__":
+    from collections.abc import AsyncIterable
+    from pynumaflow.reducer import ReduceAsyncServer, Datum, Message, Messages, Metadata
+
+    async def handler(keys: list[str], datums: AsyncIterable[Datum], md: Metadata) -> Messages:
+        counter = 0
+        interval_window = md.interval_window
+        async for _ in datums:
+            counter += 1
+        msg = (
+            f"counter:{counter} interval_window_start:{interval_window.start} "
+            f"interval_window_end:{interval_window.end}"
+        )
+        return Messages(Message(str.encode(msg), keys=keys))
+
+    if __name__ == "__main__":
         # Here we are using the function as the reducer_instance
         # which will be used to invoke the handler function.
         grpc_server = ReduceAsyncServer(handler)
         grpc_server.start()
     ```
-
-