Add support for proxy np.flatiter objects (#16107)

Closes #15388

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

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

URL: #16107

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

@@ -129,6 +129,19 @@ def wrap_ndarray(cls, arr: cupy.ndarray | numpy.ndarray, constructor):
     },
 )
 
+
+flatiter = make_final_proxy_type(
+    "flatiter",
+    cupy.flatiter,
+    numpy.flatiter,
+    fast_to_slow=lambda fast: cupy.asnumpy(fast.base).flat,
+    slow_to_fast=lambda slow: cupy.asarray(slow).flat,
+    additional_attributes={
+        "__array__": array_method,
+    },
+)
+
+
 # Mapping flags between slow and fast types
 _ndarray_flags = make_intermediate_proxy_type(
     "_ndarray_flags",

python/cudf/cudf_pandas_tests/test_cudf_pandas.py

@@ -1535,6 +1535,16 @@ def test_is_proxy_object():
     assert not is_proxy_object(s2)
 
 
+def test_numpy_cupy_flatiter(series):
+    cp = pytest.importorskip("cupy")
+
+    _, s = series
+    arr = s.values
+
+    assert type(arr.flat._fsproxy_fast) == cp.flatiter
+    assert type(arr.flat._fsproxy_slow) == np.flatiter
+
+
 def test_arrow_string_arrays():
     cu_s = xpd.Series(["a", "b", "c"])
     pd_s = pd.Series(["a", "b", "c"])