GEF: Simplify Layering of ScaledGraphics

[akoch-yatta]

GEF currently represents scaled layers using multiple nested instances of ScaledGraphics, each applying its own scale transform and forwarding drawing operations to the next level. Because much of the involved API is based on integers, this layering introduces the risk of rounding errors, particularly when several independent scale factors accumulate.

The goal of this issue is to reduce complexity by unifying multiple ScaledGraphics layers into a single instance, effectively concatenating all zoom levels into one.

It must be ensured that*all operations applied to individual layers continue to behave consistently, regardless of whether scaling is applied through separate ScaledGraphics instances (as is currently done) or through a merged, concatenated instance.