Add single-layer-pepo reduced densitymatrix

[lkdvos]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/algorithms/contractions/localoperator.jl	94.54%	3 Missing ⚠️

Files with missing lines	Coverage Δ
src/algorithms/toolbox.jl	98.38% <100.00%> (+0.08%)	⬆️
src/operators/infinitepepo.jl	64.58% <100.00%> (+2.72%)	⬆️
src/operators/localoperator.jl	89.09% <100.00%> (ø)
src/algorithms/contractions/localoperator.jl	94.98% <94.54%> (+16.40%)	⬆️

... and 1 file with indirect coverage changes

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[Yue-Zhengyuan]

I've added tests on contract_local_operator and contract_local_norm (I think these are relevant only for PEPS expectation values), and fixed some space mismatch errors caused by wrong generated @tensor indices.

[lkdvos]

Thanks for putting that together and fixing this. I don't have too much time this week, so if you want to change the error messages to be more informative and merge this, I'm definitely happy with that.

[Yue-Zhengyuan]

I have made some minor changes to the docstring and error messages. The format check error seems to be an issue with GitHub. OK to merge for me now.

[lkdvos]

Should resolve itself in a bit, I'll try and retrigger the workflows this afternoon.

julia-actions/setup-julia#350

I just found out there are issues with PEPOs with a non-trivial unit cell. I'll try to fix it.

[Yue-Zhengyuan]

I changed physicalspace for PEPO to return the physical codomain space in the bottom layer directly as a Nrow x Ncol matrix (no 3rd dimension). The original implementation returns something strange (e.g. for an 2 x 2 x 1 PEPO, it returns a length-2 vector). Things should be fine now. @lkdvos You may want to take a final look before merging.