[Python AIO] Add note for read/write APIs (#35598)

Fix: https://github.com/grpc/grpc/issues/35061

Add note to indicate that iterator and read/write APIs can't be mixed in a single RPC.

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Closes #35598

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35598 from XuanWang-Amos:aio_mix_apis_doc 4c4cfbf06e
PiperOrigin-RevId: 601580411

src/python/grpcio/grpc/aio/_base_call.py

@@ -169,6 +169,9 @@ class UnaryStreamCall(
         Read operations must be serialized when called from multiple
         coroutines.
 
+        Note that the iterator and read/write APIs may not be mixed on
+        a single RPC.
+
         Returns:
           A response message, or an `grpc.aio.EOF` to indicate the end of the
           stream.
@@ -182,6 +185,9 @@ class StreamUnaryCall(
     async def write(self, request: RequestType) -> None:
         """Writes one message to the stream.
 
+        Note that the iterator and read/write APIs may not be mixed on
+        a single RPC.
+
         Raises:
           An RpcError exception if the write failed.
         """
@@ -223,6 +229,9 @@ class StreamStreamCall(
         Read operations must be serialized when called from multiple
         coroutines.
 
+        Note that the iterator and read/write APIs may not be mixed on
+        a single RPC.
+
         Returns:
           A response message, or an `grpc.aio.EOF` to indicate the end of the
           stream.
@@ -232,6 +241,9 @@ class StreamStreamCall(
     async def write(self, request: RequestType) -> None:
         """Writes one message to the stream.
 
+        Note that the iterator and read/write APIs may not be mixed on
+        a single RPC.
+
         Raises:
           An RpcError exception if the write failed.
         """