DPAK: Fix 3d models, fix paste pads, simplify Rect/Polygon nodes

This is a minor fix and simplification of the TO_SOT_SMD generated parts:

• Fix a missing .3dshapes in the model path (curse of the copypasta, siren song of FootprintGenerator in the distance)
• Use Rect and Polygon nodes rather than the compound nodes that draw each segment as a separate line
• Remove the FCu layer from the paste pads, which stops them showing up as numbered (as noted in kicad-footprints#2677)

Also, a change that produces absolutely zero output diffs, but slightly tidies things up in the code (which needs further fairly major refactoring)

• Minor refactoring of the logic to use radius handler objects and values from global config rather than hardcodes

There's also a tiny formatting change in generator.py (which seems not to set off the pipeline check, so might be a version thing(?)

Not fixed here: the paste pads are far too big. But this is a more involved fix that I'd like to do properly in one go than hack it now.

Validations:

• No changes in output metrics (FP count or lib count)
• Only v9 format and non-visually different changes
• Tests pass

Suggest not to squash.

Output MR: kicad-footprints!4005 (merged)