fix(sheet): a box or cylinder cut along the sheet normal is flat machining (#541) (#550)

A Box cut, or a Cylinder cut whose axis is the sheet's normal, machines a sheet metal body like the extrude cut of its footprint: through the sheet it's a cut-out (a cylinder an exact round one in the flat pattern and DXF), part way it's a pocket. Primitives at other angles or across a bend are still refused. Un-ignores the #541 regression test. Fixes #541.

Co-authored-by: jonaswre <[email protected]>

docs/book/src/guide/sheet-metal.md

@@ -89,6 +89,10 @@ remain one logical sheet group through Unfold / Refold and export as separate fl
 Large profiles that exceed the geometry processing budget report an error instead of
 exporting a partial outline.
 
+A Box cut, or a Cylinder cut whose axis is the sheet's normal, machines the sheet like the
+extrude of its footprint: through the sheet it is a cut-out (a cylinder a round one), and
+part way it is a pocket. A primitive cut at any other angle, or across a folded bend, is refused.
+
 Parallel, untapered extrude cuts also preserve shallow pockets through Unfold / Refold.
 The pocket floor and side walls remain solid geometry; overlapping cuts from opposite sides
 become a through hole wherever they remove the whole thickness. Flat-pattern JSON lists