Einsum

[dc-dc-dc]

Proposed changes

Back with a path 😁

Took the feedback from the first PR and came back to this problem. Heavily inspired from numpy's optimal path algo, separated the logic to it's own file and added some testing around it. Now we have a more efficient algo that attempts to utilize tensordot whenever possible and defaulting to the previous implementation which I have renamed to einsum_naive. In draft mode for now as I have just gotten most of the tests to pass but still want to go back through the code and simplify wherever possible.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[angeloskath]

@dc-dc-dc this has not been forgotten, just bear with us as we get through PRs and new features. Big PRs like this require a little more time and clearer mind.