Expose from_dlpack on __array_namespace__()

[adityasingh2400]

Proposed changes

#3484 reports that from_dlpack and asarray(copy=) are missing from the array-api namespace returned by array.__array_namespace__(). PR #3510 wired in asarray(copy=) but explicitly deferred from_dlpack until #3495 reworked DLPack consumption. #3495 has since landed, so this PR finishes the job.

Adds a top-level mx.from_dlpack(x, *, device=None, copy=None) that delegates to the existing array-construction path. Because __array_namespace__() returns the mlx.core module, no extra wiring is needed — the new function is picked up automatically by xp.from_dlpack(...). device and copy=False raise ValueError, mirroring the array-api guarantees that MLX can honor today (MLX has no device targeting for DLPack imports and no zero-copy view).

Repro from the issue now works:

>>> import mlx.core as mx
>>> mx.array([[0, 1], [2, 3]]).__array_namespace__().from_dlpack
<built-in method from_dlpack of ...>

Checklist

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

Fixes #3484.

[zcbenz]

Thanks for the PR! This is covered by #3531 which is being worked on.