Forward AD rules and tests for polar decompositions

[kshyatt]

This seems to just work out of the box without hacking at special tangents or anything, so why not add...

[kshyatt]

🎉 CUDA tests are passing 🎉

[codecov]

Codecov Report

❌ Patch coverage is 80.35714% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ixAlgebraKitEnzymeExt/MatrixAlgebraKitEnzymeExt.jl	0.00%	11 Missing ⚠️

Files with missing lines	Coverage Δ
...gebraKitMooncakeExt/MatrixAlgebraKitMooncakeExt.jl	65.24% <100.00%> (+1.55%)	⬆️
src/MatrixAlgebraKit.jl	100.00% <ø> (ø)
src/pushforwards/polar.jl	100.00% <100.00%> (ø)
...ixAlgebraKitEnzymeExt/MatrixAlgebraKitEnzymeExt.jl	0.00% <0.00%> (ø)

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[lkdvos]

Left some suggestions about performance but otherwise looks great!!

[kshyatt]

Left some suggestions about performance but otherwise looks great!!

I wrote this in a less performant way but clearer to me way at the start just to make sure it was correct, thanks for the suggestions! Think I got everything in both push-forwards.

[lkdvos]

It might even be worth it to add a comment to the implementations with the actual math for the formulas, you are right that it is way harder to follow what is going on now

[kshyatt]

We don't have that right now for other pullbacks so I am ok with this as-is, would be good to go through all of them at some point and add this though. I think the fail is unrelated, I'm going to merge.