feat: drag a fillet's radius spline by its handles on the edge (#752)

A spline fillet's radius can now be dragged by handles on the edge, and the spline radius saves under format 17.

crates/doc/src/assembly.rs

@@ -227,7 +227,7 @@ impl FeatureKind {
             }
             FeatureKind::Fillet { edges, style, .. } => {
                 edges.iter_mut().for_each(pt);
-                if let crate::FilletStyle::Variable { start, .. } = style {
+                if let crate::FilletStyle::Variable { start, .. } | crate::FilletStyle::Spline { start, .. } = style {
                     pt(start);
                 }
             }