Move the Rectangles engine's global and ordered pick loops into
RectanglePacking.MaxRectsPacker, which works on plain box sizes so other
fill paths can reuse it. SheetPacker maps part orientations onto it.
No behavior change: rectangle-lane benchmark results are identical job for
job (91 strict and 77 boxable jobs).
MaxRectsSheet only tracks free rectangles and has no job dependencies, so it
moves from the Rectangles engine into OpenNest.Engine.RectanglePacking where
the interactive fill packer can use it. No behavior change.
Moves the two production plug-in engines into OpenNest.Engine under names
that describe the jobs they suit:
- Rectangles: plain and near-rectangular plates, maximal-rectangles box
packing (was the RectanglesNestingEngine plug-in)
- Irregular: irregular profiles, no-fit-polygon frontier packing (was the
Opus55NestingEngine plug-in)
Their tests and the shared engine contract/layout test kit move into
OpenNest.Engine.Tests/NestingEngines.
The registry maps the old plug-in names to the new engines, so saved desktop
selections, scripts and API requests keep working, and a leftover plug-in DLL
under an old name cannot shadow its replacement. Desktop startup passes the
registry's lookup when restoring the saved Auto Nest engine.
aj