aten.unbind exports to Sequence ops

[yuanyao-nv]

For the following line in model definition:

x1, x2 = hidden_states.unflatten(-1, (-1, 2)).unbind(-1)

onnxscript translates the aten.unbind op to Sequence ops:

In the case of static shapes, I think it should be possible to translate to a regular Split op instead? Would it be possible to add a rewrite pattern for this case?

The motivating use case comes from the Wan2.2 model definition: https://github.com/huggingface/diffusers/blob/9ae5b6299d3b1a7b0378dc77c3c69baf521587d2/src/diffusers/models/transformers/transformer_wan.py#L109

[justinchuby]

@gramalingam @titaiwangms

[justinchuby]

I guess we can emit Split in the aten op impl too when shapes are static.

[justinchuby]

Can you try #2597

[yuanyao-nv]

Thanks #2597 fixes it.