[WIP] Allow turning off allowscalar copies for yacusolver

[kshyatt]

The idea of this PR is to make the checks involving @allowscalar optional. These copies are extremely expensive and block the device, so by (optionally) disabling them, we should be able to make better use of the GPU.

So far I've just done the CUSOLVER ones, but I can also do ROCSOLVER if we like the idea. I think it would make sense to have a settable flag that turns the checks on and off so that users can control it, or a CheckedCUSOLVER driver. Anyone have thoughts on that angle?

[lkdvos]

Definitely looks reasonable to me, although it would be nice to get a sense of how bad the performance is to try and decide if we want to turn this on or off by default.

Is this specifically for the case where we apply the factorizations to a bunch of blocks and don't want to sync inbetween? There might also be a case for writing a batched version that tries to only sync at the end or something similar

[kshyatt]

Is this specifically for the case where we apply the factorizations to a bunch of blocks and don't want to sync inbetween?

Indeed it helps with this but not only here, another example is calc_convergence in PEPSKit where we're computing svd_vals 8 times (4 corners, 4 edges).

[lkdvos]

Yeah fair enough, I definitely think the keyword argument is a good solution, just slightly on the fence about disabling checks by default. 🤷 it's a bit annoying to think that PEPSKit would run without these and then if at some point something doesn't converge it just silently goes haywire, and then you have to do a full rerun with checks on to figure out what happened, but I guess that's what it has to be

[kshyatt]

I agree, that's why I think in fact this should be settable at __init__ or with an env var. But what to call it?

[codecov]

Codecov Report

❌ Patch coverage is 36.36364% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ext/MatrixAlgebraKitCUDAExt/yacusolver.jl	36.36%	14 Missing ⚠️

Files with missing lines	Coverage Δ
ext/MatrixAlgebraKitCUDAExt/yacusolver.jl	90.94% <36.36%> (-5.19%)	⬇️

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