Declare a different name for nan_equality.UNEQUAL to prevent Cython w…

…arnings. (#12947)

Closes #9462.

```
warning: cudf/_lib/cpp/types.pxd:51:8: 'UNEQUAL' redeclared
```

We've been dealing with warnings like this for as long as I've worked on cudf. I think it'd be good to fix this by renaming the Cython enum. We don't rely on this name very much at the Cython/Python level, so it's a small change. (This has been irking me for a long time and I want to see this warning go away in the build logs.)

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - https://github.com/brandon-b-miller

URL: #12947

python/cudf/cudf/_lib/cpp/types.pxd

@@ -1,4 +1,4 @@
-# Copyright (c) 2020-2022, NVIDIA CORPORATION.
+# Copyright (c) 2020-2023, NVIDIA CORPORATION.
 
 from libc.stdint cimport int32_t, uint32_t
 
@@ -47,8 +47,10 @@ cdef extern from "cudf/types.hpp" namespace "cudf" nogil:
         UNEQUAL "cudf::null_equality::UNEQUAL"
 
     ctypedef enum nan_equality "cudf::nan_equality":
+        # These names differ from the C++ names due to Cython warnings if
+        # "UNEQUAL" is declared by both null_equality and nan_equality.
         ALL_EQUAL "cudf::nan_equality::ALL_EQUAL"
-        UNEQUAL "cudf::nan_equality::UNEQUAL"
+        NANS_UNEQUAL "cudf::nan_equality::UNEQUAL"
 
     ctypedef enum type_id "cudf::type_id":
         EMPTY                  "cudf::type_id::EMPTY"

python/cudf/cudf/_lib/lists.pyx

@@ -1,4 +1,4 @@
-# Copyright (c) 2021-2022, NVIDIA CORPORATION.
+# Copyright (c) 2021-2023, NVIDIA CORPORATION.
 
 from cudf.core.buffer import acquire_spill_lock
 
@@ -84,7 +84,7 @@ def distinct(Column col, bool nulls_equal, bool nans_all_equal):
         null_equality.EQUAL if nulls_equal else null_equality.UNEQUAL
     )
     cdef nan_equality c_nans_equal = (
-        nan_equality.ALL_EQUAL if nans_all_equal else nan_equality.UNEQUAL
+        nan_equality.ALL_EQUAL if nans_all_equal else nan_equality.NANS_UNEQUAL
     )
 
     cdef unique_ptr[column] c_result