Add Neighborhood Tensor Update (NTU)

[Yue-Zhengyuan]

This PR adds the construction of bond environments using neighboring tensors and Schmidt weights of a bond. They are intended to be used in Neighborhood Tensor Update for InfiniteWeightPEPS. The code is adapted from YASTN, and I have put the credit in src/algorithms/contractions/bondenv/benv_ntu.jl.

TODO

• The direction names t/l/b/r are directly borrowed from YASTN, and need to be changed to north, west, south, east to follow PEPSKit convention after everything else have been figured out.
• Determine the best codomain/domain choice for the PEPSOrths (the X and Y tensors) that can reduce the number of permutes and twists.
• enlarge_corner_se, enlarge_corner_nw may reuse functions in existing CTMRG code.

[codecov]

Codecov Report

❌ Patch coverage is 83.54430% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/algorithms/contractions/bondenv/benv_tools.jl	82.35%	9 Missing ⚠️
src/algorithms/contractions/bondenv/benv_ntu.jl	85.71%	4 Missing ⚠️

Files with missing lines	Coverage Δ
src/PEPSKit.jl	100.00% <ø> (ø)
src/algorithms/contractions/bondenv/benv_ntu.jl	85.71% <85.71%> (ø)
src/algorithms/contractions/bondenv/benv_tools.jl	82.35% <82.35%> (ø)

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