feat: Improvements to Elaboration of tensor expressions

[jstoobysmith]

Two improvements to Elaboration of tensor expressions:

• Terms of type Tensor S _ now no longer get a redundant toTensor inserted when they appear in tensor expressions.
• Redundant permutations of indices (which trivially correspond to the identity) are no longer added.

co-authored with claude.

[github-actions]

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[morrison-daniel]

Looks good