Fix Oklab from Oklch hue conversion

[tomcur]

The Oklch -> Oklab conversion currently inverts the hue by swapping the a and b components. This PR corrects the calculation and adds an Oklch -> Oklab -> Oklch roundtrip test.

[Ogeon]

Hi, thank you for spotting this and for taking the time to fix it (with added tests too!). It may have been a naming confusion when replacing sin_cos. Either way, I'll let the tests run through, but it looks good to me. 👍

[Ogeon]

Alright, it's all green, so let's merge this.

bors r+

[bors]

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• ci

[tomcur]

Thank you for the quick merge!

[wash2]

Is there planned to be a release with this fix?

[Ogeon]

I'll try to get it out within the next few days. I was initially going to add CAM16 (#342) in the same release, but it turned out to be a bit trickier than expected. I'll put it to the side for a bit and add a couple of missing casting traits, and then make the release.