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.