Add the fast type to the NamedAgg wrapper in cudf.pandas (#21135)

Authors:
  - Matthew Murray (https://github.com/Matt711)

Approvers:
  - Matthew Roeschke (https://github.com/mroeschke)

URL: #21135

Author: Matt711

python/cudf/cudf/pandas/_wrappers/pandas.py

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
+# SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 import abc
 import copyreg
@@ -2068,10 +2068,10 @@ def holiday_calendar_factory_wrapper(*args, **kwargs):
 
 NamedAgg = make_final_proxy_type(
     "NamedAgg",
-    _Unusable,
     pd.NamedAgg,
-    fast_to_slow=_Unusable(),
-    slow_to_fast=_Unusable(),
+    pd.NamedAgg,
+    fast_to_slow=lambda fast: fast,
+    slow_to_fast=lambda slow: slow,
     additional_attributes={
         "__hash__": _FastSlowAttribute("__hash__"),
     },

python/cudf/cudf_pandas_tests/test_cudf_pandas_no_fallback.py

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2024-2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
+# SPDX-FileCopyrightText: Copyright (c) 2024-2026, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
 import pytest
@@ -151,3 +151,11 @@ def test_no_fallback_in_memory_usage_and_sizeof(dataframe, series):
     with pytest.warns(UserWarning, match="The deep parameter is ignored"):
         i.memory_usage(deep=True)
         i.__sizeof__()
+
+
+def test_no_fallback_in_named_agg(dataframe):
+    df = dataframe
+    df.groupby("a").agg(
+        min_b=pd.NamedAgg(column="b", aggfunc="min"),
+        max_c=pd.NamedAgg(column="c", aggfunc="max"),
+    )