Sheet metal: sheet.perforate, a perforation field exported to the flat pattern and DXF (#732) (#1041)

Adds sheet.perforate: round holes on a staggered or square grid over the flat sheet, kept clear of edges, cut-outs and bend zones. The holes go to the flat pattern, the DXF and the measured volume rather than the B-rep, so a panel can carry many thousands of them.

crates/doc/src/params.rs

@@ -323,6 +323,13 @@ macro_rules! feature_walk {
                         f("Gap", g, L, I);
                     }
                 }
+                FeatureKind::SheetPerforate { diameter, pitch, margin, .. } => {
+                    f("Diameter", diameter, L, I);
+                    f("Pitch", pitch, L, I);
+                    if let Some(m) = margin {
+                        f("Margin", m, L, I);
+                    }
+                }
                 FeatureKind::Coil { diameter, pitch, turns, section_size, start_angle, base, .. } => {
                     f("Diameter", diameter, L, I);
                     f("Pitch", pitch, L, I);