Remove unnecessary type restriction on _safe_pow

[pbrehmer]

Here we loosen the restriction of the number type in _safe_pow. This makes sense since sdiag_pow should also work on complex diagonal tensor maps. (I need this for a niche application related to differentiating the SVD which has to do with extra phase freedom for complex SVDs.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
src/utility/util.jl	51.00% <100.00%> (ø)

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[lkdvos]

Somehow the tests all ran out of time again, while this really shouldn't have changed anything. Any clue?

[pbrehmer]

Whoops that is really weird, I really have no idea why that should change anything. Perhaps that changed precompilation times? In any case that shouldn't make such a big difference. I'll try to find some time tomorrow...

Edit: Or perhaps the CI ran on new package versions which changed execution/precompilation times significantly.

[lkdvos]

Seems like this is unrelated to this change, so I'm okay with just merging this and trying to fix the time-outs in a different PR

[pbrehmer]

Alright, that's certainly fine by me. Then I would think the time-outs are related to different package versions.

[leburgel]

Seems like a Zygote thing, CI was running Zugote v0.7.5 here versus v0.7.4 in the latest run where all the tests passed.