Fix oklab/oklch lightness misparsed as percentage when given as a number

[scasteran-jw]

Types of Changes

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Description

Summary

oklab()/oklch() accept the L (lightness) component as either a <percentage>
or a plain <number>. Per the CSS Color 4 spec, the percentage reference range
0%–100% maps to a number range of 0–1 (e.g. 40.1% ≡ 0.401).

The parser treated both forms identically, passing the raw parsed value straight
into CssColorValue.FromOklab, which expects L in [0,100] and internally
divides by 100. Percentages worked (40.1% → 40.1), but numbers didn't
(0.401 stayed 0.401 → scaled down to 0.00401), producing a near-black
color instead of the intended one.

Fix

ParseLabComponent in ColorParser.cs now takes an optional numberScale
factor applied only to the unitless/number form (percentages are unaffected).
ParseOklab/ParseOklch pass numberScale: 100.0 for their L component so
0.401 is normalized to 40.1, matching 40.1%.

lab()/lch() and the a/b/c/h components of all four functions were
left untouched — their number and percentage forms already share the same
native range per spec, and no failing test indicated an issue there.

Testing

• Added ParseOklchNumberToRgb_First/_Second and ParseOklabNumberToRgb_First/_Second,
  asserting the number form produces the same RGB output as the existing
  percentage-form tests.
• Full test suite: 1999/1999 passing.

[CLAassistant]

All committers have signed the CLA.

[FlorianRappl]

LGTM!