Fix trace for PyTorch backend

[merajhashemi]

Currently, the trace operator for PyTorch only supports up to 25-dimensional inputs due to using einsum. This PR fixes this issue.

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[merajhashemi]

@googlebot I signed it!

[mganahl]

@merajhashemi thanks for the PR. Looks good from my side. The build error is some flaky in the jax-backend. Let me first fix this test and we'll merge this in then.