BlockTensorMap

[lkdvos]

This PR contains a (rather large) amount of breaking changes, by factoring out a large amount of code into a separate package. In particular, we now rely on BlockTensorKit to deal with the logic of (sparse) block MPO tensors and environments, which simplifies the code here quite a bit.

Additionally, many parts of the code have been cleaned up and renamed, so this change should be considered very breaking.

TODO

• port over last changes from current master
• release last fixes for current version, since we will have to release a new minor version
• verify if there are additional checks that can be done to ensure everything is still behaving as required

[Gertian]

Thanks, that exactly what I was after :)
I started looking and saw that most changes were very minor, so I wanted to know where the relevant changes where.
I should have worded that better.

Do you want me to mark things that I find unclear ?

[lkdvos]

It depends a bit, if it's user-side things that are unclear, yes. If it's implementation-side things, maybe, but probably not. While I value clarity and readability, I don't have the time to make sure the implementations are always as clear as possible, since MPSKit is not really meant to be educational...

[lkdvos]

Unless there are strong opinions against this, I will merge this tomorrow, and keep track of the todos before release in the discussions. The idea is that this PR is a monster, and it's hard to keep an overview of what's going on. There are a few concrete things left to do, which will be easier to track in separate PRs.