BitmaskLabels : disable darkening of the area outside the bitmask when selected

**Is your feature request related to a problem? Please describe.**
When a Bitmask is selected (e.g., right after painting an area), the area outside the mask is darkened. This makes it extremely difficult to refine existing bitmasks on already dark images, such as ultrasound images, as the dark overlay hides important details.
Since segmentation usually requires multiple refinement steps rather than a single pass, this behavior is very impractical.

**Describe the solution you'd like**
Add an option to disable the dark overlay outside the active bitmask. Alternatively, remove or adjust this behavior if it’s not essential to most users.

**Describe alternatives you've considered**
Adjusting contrast and brightness each time I edit a bitmask, but this is inefficient.
Using BrushLabels, but I need precise pixel-wise segmentation, so they aren’t suitable. Additionally, BrushLabels have their own issues (e.g., the brush cursor size not updating when zooming).

**Additional context**