Preserve color space on Saturation changes (Consistency with Hue and Luminance traits)

[coreh]

Objective

• Make the Saturation trait match the behavior of Hue and Luminance traits, by preserving the underlying color space of the modified color

Solution

• Assign to the interior mutably borrowed value in the underlying color space, instead of just returning a new value in an arbitrary color space (Color::Hsla())

Testing

• Manual testing. Trivial change, behavior already consistent with existing traits