Returns a rectangle that contains all the pixels painted by this box.
The paint bounds can be larger or smaller than size, which is the amount of space this box takes up during layout. For example, if this box casts a shadow, that shadow might extend beyond the space allocated to this box during layout.
The paint bounds are used to size the buffers into which this box paints. If the box attempts to paints outside its paint bounds, there might not be enough memory allocated to represent the box's visual appearance, which can lead to undefined behavior.
The returned paint bounds are in the local coordinate system of this box.
@override Rect get paintBounds => Offset.zero & size;