einsum type instability #22
Description
See under-Peter/OMEinsum.jl#97.
Type stability is important for e.g. Reactant compilation iirc, see #12. May consider wrapping TensorOperations.jl if that is any better. The truth might be that the einops notation for einsum isn't optimal for Julia, and you can get farther with TensorOperations.jl or OMEinsum.jl alone.
Need tests to track general type instability, see #21.