Implement something like torch.einsum for Tensors

[TheLostLambda]

Feature description

Something like https://pytorch.org/docs/stable/generated/torch.einsum.html, with something similar done in Rust already here: https://docs.rs/einsum-codegen/latest/einsum_codegen/

Feature motivation

It's a more compact way to write out a number of tensor operations that come up throughout ML work.

(Optional) Suggest a Solution

It seems like a good place for writing a macro! It looks like there are some details on the algorithm here: https://docs.rs/einsum-codegen/latest/einsum_codegen/#einsum-algorithm