ENH: test nextafter

[ev-br]

towards #299

[ev-br]

Merging straight away so that data-apis/array-api-compat#306 can run it across backends.

[crusaderky]

Missing test case for Python scalars (with ad-hoc behaviour when the python scalar is x1)

[ev-br]

Missing test case for Python scalars (with ad-hoc behaviour when the python scalar is x1)

Not really:

$ git diff
diff --git a/array_api_tests/test_operators_and_elementwise_functions.py b/array_api_tests/test_operators_and_elementwise_functions.py
index 6b4e555..2f9d9b7 100644
--- a/array_api_tests/test_operators_and_elementwise_functions.py
+++ b/array_api_tests/test_operators_and_elementwise_functions.py
@@ -1850,6 +1850,8 @@ def _filter_zero(x):
 )
 @given(x1x2=hh.array_and_py_scalar(dh.real_float_dtypes))
 def test_binary_with_scalars_real(func_data, x1x2):
+    if isinstance(x1x2[0], float):
+        breakpoint()
     _check_binary_with_scalars(func_data, x1x2)

stops with

-> _check_binary_with_scalars(func_data, x1x2)
(Pdb) p x1x2
(63.0, tensor([[ 0.6733,  0.3333, 26.0324,  1.9000]]))

int scalars, are missing yes. This is on par with testing other binary functions.