fix: coerce NaN Lab/OKLab channels to 0 in parseColor

[sarathfrancis90]

Summary

Fixes#317.

color-mix() is resolved at compile time by lightningcss. For a degenerate
mix the result can have NaN chromaticity channels — mixing #000 with
transparent in oklab gives oklab(0 NaN NaN / 0.5), because black has no
chromaticity to interpolate. parseColor passed those NaN coords straight
to colorjs.io, which serialized them to "#NaNNaNNaN80". React Native
silently discards an invalid color string, so utilities like Tailwind's
bg-black/50 rendered with no background.

Fix

The lab/lch/oklab/oklch cases in parseColor (src/compiler/declarations.ts)
now coerce each channel through a small nanToZero helper. A missing color
component is 0 per CSS Color 4, so oklab(0 NaN NaN / 0.5) becomes
oklab(0 0 0 / 0.5) = black at 50% alpha, serializing to #00000080.

Testing

Added a regression test in src/__tests__/native/color-mix.test.tsx for
color-mix(in oklab, #000 50%, transparent). It fails on main
(Received "#NaNNaNNaN80") and passes with the fix ("#00000080").

yarn test, yarn typecheck and yarn lint all pass.

[danstepanov]

@sarathfrancis90 thanks for opening a PR, can you rebase with the main branch?

[sarathfrancis90]

Rebased onto main — should be clean now. Thanks!

[danstepanov]

Preemptive review to help triage for the 5.0 release, @marklawlor makes the final call.

Verified against current main and it holds up. Tailwind compiles bg-black/50 to a color-mix that lightningcss resolves to NaN oklab channels, and parseColor passed them through so RN got #NaNNaNNaN80 and dropped the style. Coercing NaN to 0 matches CSS Color 4 missing component semantics, the regression test fails on main without the fix, and the diff applies cleanly. Works on v4, silently broken on v5, so I'd call it a blocker for latest.

[sarathfrancis90]

Thanks for the detailed review @danstepanov, really appreciate it. I've rebased onto the latest main and everything's still green, so it should be good to go for the 5.0 triage — happy to adjust anything if @marklawlor wants changes.

[danstepanov]

On my merge list for today!