Implement Kronecker product

[emmatyping]

Picking up from #1039 and based on my original implementation in #652 with the feedback from @bluss.

I found this implementation performs the same vs #1039 modulo using uninit, at least for my use case.

[emmatyping]

Also I should mention that I kept the name as kron because that is what numpy and matlab use and it seems familiar.

[emmatyping]

Hm, I just noticed there is also #690. Not sure what direction you want to go, but happy to work on getting an outer based implementation in if that's preferable.

[bluss]

I don't have so much opinions about what's best here - this is outside my area.

It's easier if we maybe see it like this, some of the numerics stuff is not my area, and then it needs help from others to design and maybe even merge it, we maybe need a maintainer who likes that area. 🙂 I'm mainly focusing on certain things. It doesn't mean the other things are not good, just not my focus & interest.

[bluss]

Thanks! Please keep this comment here in mind #1105 (review) - we need a maintainer for "this area" (deeper numerical functions) - also collaboration with the ndarray-linalg crate.

[emmatyping]

@bluss yes, I'd be happy to keep contributing and maintaining this area! I sent a message on matrix to follow up :)