a_pan_moves_the_marks_without_building_them covered Direct Selection
only. It now runs with both tools.
The module comment and MAX_PAN's comment now say what is kept as
triangles and as document points, and when a pan builds the marks again.
A test label now says points rather than px.
The timings in docs/target-app-parity.md are measured again with 10 fill
colors on the 2,000 circles. The pixel sentence there also names the
rounding errors of kept vertices.