Handle ND secret tensors in insert-rotate

[j2kun]

#587 identified that we may need to determine how to handle multidimensional secret inputs in insert-rotate or upstream of it.

Just brainstorming: it seems like what we would want to do is determine in advance of insert-rotate how to convert multidimensional tensors to 1D tensors. Perhaps that means we take any ND function inputs and add reshape ops at the very beginning and end, though that would have a pretty large effect on the intermediate IR, requiring one to convert any tensor index-accessing ops to the corresponding flattened version. Even so, we must have gotten most, if not all, of the hard work done when we did this for verilog codegen. We can probably reuse that.

[j2kun]

I think the SIMD packing work will handle this. Optimistically closing.

[asraa]

I'll update the SIMD packing to clarify the ND case as a TODO - we talked a little about collapsing tensors as well, and I need to recap that discussion in the issue.