DrawSaturation walked the whole saturated set adding two QGraphicsLineItems
each, with none of the viewport culling DrawSpots and DrawPredictions do
directly above it, and no upper bound - and it is rebuilt on every pan,
zoom and frame change. Unlike spots, that set is not bounded by a setting:
an over-exposed frame or a missing beamstop saturates a large fraction of
the detector, which meant hundreds of thousands of scene items and a
multi-second freeze on each mouse drag.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>