fix(oklab, oklch, gl): default alpha to 1 when it is omitted

[abhu85]

Colors built through the oklab, oklch or gl constructors without an explicit alpha end up with an alpha of NaN:

chroma.oklch(0.5, 0.1, 20).alpha()       // NaN
chroma.oklch(0.5, 0.1, 20).hex('rgba')   // '#944a4baN'
chroma.mix(chroma.oklch(0.5, 0.1, 20), 'red')
// on main, since #399: Error: invalid rgb color

oklab2rgb and oklch2rgb (like the gl input) return only [r, g, b] for opaque colors. clip_rgb then always clamped index 3, which turned the missing value into NaN before the Color constructor could default it to 1. The if (me._rgb.length === 3) me._rgb.push(1) fallback therefore never ran for these inputs.

This PR makes clip_rgb clamp alpha only when it is present, so the constructor's default applies. The other clip_rgb callers (average, cubehelix) always pass four values and are unaffected, and _unclipped is copied before the loop, so it is unchanged.

Tests: added two cases to test/alpha.test.js for the alpha default and for mixing/scaling such a color; both fail without the change. Full vitest suite: 2534 passing. A changeset is included.

[changeset-bot]

🦋 Changeset detected

Latest commit: 64a8897

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
chroma-js	Patch

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