Add BaseOffset as a final proxy type to pass instancechecks for offse…

…ts against `BaseOffset` (#14678)

Addresses part of #14674.

This PR makes `cudf.pandas` aware of the `BaseOffset` type. Because of the way `isinstance()` checks work on proxy types*, we will now pass instance checks like:

```python
freq = "D"
assert isinstance(pd.tseries.frequencies.to_offset(freq), pd.tseries.offsets.BaseOffset)
```

*proxy types appear to be related to each other in the same way as their corresponding slow types. So if `A` inherits from `B`, then `ProxyA` _appears_ to inherit from `ProxyB` even though they are not _actually_ related by inheritance.

Authors:
  - Ashwin Srinath (https://github.com/shwina)
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #14678

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

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2023 NVIDIA CORPORATION & AFFILIATES.
+# SPDX-FileCopyrightText: Copyright (c) 2023-2024 NVIDIA CORPORATION & AFFILIATES.
 # All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 import copyreg
@@ -1036,6 +1036,15 @@ def _df_query_method(self, *args, local_dict=None, global_dict=None, **kwargs):
     additional_attributes={"__hash__": _FastSlowAttribute("__hash__")},
 )
 
+BaseOffset = make_final_proxy_type(
+    "BaseOffset",
+    _Unusable,
+    pd.offsets.BaseOffset,
+    fast_to_slow=_Unusable(),
+    slow_to_fast=_Unusable(),
+    additional_attributes={"__hash__": _FastSlowAttribute("__hash__")},
+)
+
 Day = make_final_proxy_type(
     "Day",
     _Unusable,

python/cudf/cudf_pandas_tests/test_cudf_pandas.py

@@ -1233,3 +1233,8 @@ def test_concat_fast():
 def test_func_namespace():
     # note: this test is sensitive to Pandas' internal module layout
     assert xpd.concat is xpd.core.reshape.concat.concat
+
+
+def test_isinstance_base_offset():
+    offset = xpd.tseries.frequencies.to_offset("1s")
+    assert isinstance(offset, xpd.tseries.offsets.BaseOffset)