Add native types for PHP 8.3

[guillaume-sainthillier]

Now that develop requires PHP ^8.3, the remaining untyped class constants in DominantPaletteAnalyzer and Colors\Themes\VibrantMuted\Definition are typed (private const float MIN_VIBRANT_SATURATION = 0.35), matching the rest of the codebase which already used typed constants.

Closures and arrow functions in src and tests that were missing parameter or return types now have them (e.g. drawRectangle(function (RectangleFactory $rectangle): void { ... })).

A few things worth noting:

• Collection::filter() and Palette::filter() wrappers return mixed, not bool: with strict_types=1 a bool return would throw a TypeError for user callbacks returning a truthy non-bool value, which array_filter() accepts today.
• The closures in the Colorspace::colorFromNormalized() methods are left untyped. Typing them ColorChannelInterface (what fromNormalized() returns) makes PHPStan report that the spread arguments don't match the specific channel types the Color constructors expect. Fixing that properly is a refactor rather than typing.
• Stream resources (File::$stream, FileInterface::toStream(), CanBuildStream::buildStreamOrFail(), the GD ResolutionAnalyzer handles and encoder callbacks) keep their docblock types, since PHP has no native resource type and mixed would add nothing.

No behaviour change. PHPStan and PHPCS pass.

[olivervogel]

Thanks.