Add copy keyword to mx.asarray

[eyupcanakman]

Proposed changes

mx.asarray does not accept the copy keyword from the array-API spec. References #3484.

The fix adds copy as a keyword-only argument with the spec semantics: True always copies the input, False never copies and raises ValueError if a copy would be required, and the default None keeps the existing behavior. For copy=True on an mlx array of matching dtype, the binding routes through mx::copy(arr). Note that mlx is lazy and functional, so Copy::eval calls out.copy_shared_buffer(inputs[0]); the post-eval buffer can be shared with the source until a downstream op writes a fresh allocation. This matches the existing __copy__ / __deepcopy__ semantics on mx.array.

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

Checklist

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[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.