Add copy keyword to mx.asarray

[eyupcanakman]

Proposed changes

mx.asarray doesn't accept the copy keyword from the array-API spec. References #3484.

This adds copy as a keyword-only argument. MLX has no in-place operations, so a non-copying conversion isn't meaningful: copy=False raises ValueError, and copy=True or unspecified behave the same as before.

The from_dlpack half of #3484 is left out, since PR #3495 reworks dlpack consumption through the mx.array(...) constructor and the namespace wiring depends on that landing.

Checklist

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• I have read the CONTRIBUTING document
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• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[zcbenz]

The copy parameter only makes sense if the framework supports in-place operation and you want to make a deep copy whose content would stay unchanged when the original copied array got an in-place update. But since MLX has no in-place operation and the supposed use case would never happen.

So I think the best way to support copy parameter is to simply throw when copy=False is passed and return create_array(a, dtype) otherwise like before. Because copy=False means shallow-copy which makes no sense in MLX, and code using copy=True|None would stay semantically correct.

[eyupcanakman]

Makes sense, reworked it that way: copy=False raises now, copy=True and the default go through create_array like before.

[zcbenz]

Looks good to me, thanks!