`test_dunder_dlpack` hard-pins `dl_device` to `kDLCPU`, so it fails for any non-CPU-native library

[antonwolfy]

array_api_tests/test_dlpack.py::test_dunder_dlpack always requests a CPU DLPack device while independently drawing copy ∈ {True, False, None}, and treats any exception as a failure. For a device-backed library (GPU/SYCL/etc.), the copy=False + dl_device=(kDLCPU, 0) combination forces a device→host copy that the standard requires be refused with BufferError — so the test fails on spec-compliant behavior. It only passes for libraries whose default device is already CPU.

Reproduction

The test generates:

dl_device_kw=hh.kwargs(
    dl_device=st.tuples(  # XXX: the 2023.12 standard only mandates ... kDLCPU ?
        st.just(DLPackDeviceEnum.CPU.value),   # == 1 (kDLCPU)
        st.just(0)
    )
),
...
copy_kw=hh.kwargs(copy=st.booleans() | st.none()),

and then does:

def test_dunder_dlpack(x, copy_kw, max_version_kw, dl_device_kw, data):
    try:
        x.__dlpack__(**copy_kw, **max_version_kw, **dl_device_kw)
    except Exception as exc:      # BufferError is never expected/caught
        ph.add_note(exc, repro_snippet)
        raise

For a library whose default device is not kDLCPU, Hypothesis eventually draws copy=False, and x.__dlpack__(copy=False, dl_device=(kDLCPU, 0)) raises:

BufferError: array cannot be placed on the requested device without a copy

Example failing case (from dpnp/dpctl):

x=array([], dtype=bool),
copy_kw={'copy': False},
max_version_kw={'max_version': (1, 0)},
dl_device_kw={'dl_device': (1, 0)},

[ev-br]

Ouch. Thanks for the report @antonwolfy. Would you be up to sending a PR with a fix? I'll gladly review/test.