Fix truncrank when kept rank is larger than input rank

[Yue-Zhengyuan]

This PR fixes truncrank when the rank to be kept is already larger than the input tensor, so it should be the same as notrunc. The old code breaks only when the fusion style is UniqueFusion (including Trivial and abelian symmetries).

I bumped into the issue in QuantumKitHub/PEPSKit.jl#314 for finite-T time evolution. The infinite-T PEPO D = 1, and I rely on truncrank(D) to automatically keep fewer than D singular values when possible.

There was a similar bug in eig(h)_trunc that can be solved by this PR, but I didn't add a test for it.

[Yue-Zhengyuan]

I wanted to directly short-circuit to the NoTruncation function, but then I noticed the rev option, which is absent in notrunc.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/factorizations/truncation.jl	94.40% <100.00%> (+0.03%)	⬆️

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[lkdvos]

Thanks for the fix and added test ❤️