fix: Support oklch CSS colors

[sebastianwd]

Fixes #3058

oklch() is a new way to define CSS colors. In oklch(L C H) or oklch(L C H / a), each item corresponds as follows:

L is perceived lightness (0-1). “Perceived” means that it has consistent lightness for our eyes, unlike L in hsl().
C is chroma, from gray to the most saturated color.
H is the hue angle (0-360).
a is opacity (0-1 or 0-100%).

It's the default color format for the TailwindCSS v4 and shadcn themes.

Added a oklch to rgba converter based on the implementation in the culori library

[sebastianwd]

Tests pass locally, not sure what's wrong with ci.