model: Add a clamping step in iconOnBarBackground that might be unnecessary

We'll get an error if `clamped20to75AsHsl.lightness - 0.12` ends up
being below 0.0 or above 1.0...

...which probably can't happen? The value
`clamped20to75AsHsl.lightness` is the "L" of an HSL representation
of a certain color.

That certain color is *supposed* to be the result of clamping an
*LCH* "L" value between 20 and 75...but it actually comes from
clamping a LAB color's "L" value between those numbers...but we have
a comment saying the "L" axis might be the same between LCH and
LAB...

...but I think HSL "L" probably doesn't match either LCH "L" or LAB
"L"...which still might not matter in this case? Anyway, with some
uncertainty, it seems like it might be wise to do this clamping to
avoid an error.

Author: chrisbobbe

lib/api/model/model.dart

@@ -494,7 +494,7 @@ ColorSwatch<StreamColor> streamColorSwatch(int base) {
     // TODO fix bug where our results differ from the replit's (see unit tests)
     StreamColor.iconOnBarBackground:
       clamped20to75AsHsl
-        .withLightness(clamped20to75AsHsl.lightness - 0.12)
+        .withLightness((clamped20to75AsHsl.lightness - 0.12).clamp(0.0, 1.0))
         .toColor(),
 
     // Follows `.recepient` in Vlad's replit: