[Relax][ONNX] Accept 1-D scalar inputs in NonMaxSuppression

[guan404ming]

Related Issue

closes #19693

Why

NumPy 2.x raises TypeError on int(np.array([3])), so importing an ONNX NonMaxSuppression whose scalar params are 1-D single-element tensors (shape[1], common from exporters) crashed.

How

• Cast the constant max_output_boxes_per_class / iou_threshold / score_threshold via .numpy().item(), which accepts both 0-D and 1-element tensors (matching the existing param-Var path).
• Add an import test feeding 1-D scalar constants (the default folding path that the existing test_nms misses).

[gemini-code-assist]

Code Review

This pull request updates the ONNX frontend in TVM Relax to use .numpy().item() instead of .numpy() when converting 1-D single-element constants to Python scalars, ensuring compatibility with NumPy 2.x. A test case has also been added to verify this behavior. The review feedback points out that iou_threshold is missing a relax.Var handling path in both _impl_v10 and _impl_v1 implementations, which could cause it to be silently ignored and overridden to its default value when provided as a variable.

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