Class-A surfacing 1/3: the continuity core, a G3 free-form blend and patch crown (#1249)

The continuity core (kernel bridge: Hermite control rows reproducing a support surface's position, tangent, curvature and change of curvature, G0 to G3), surface.blend between two edge chains (#764), and a crown for fitted patches. Existing patches and fillets are unchanged by default (crown 0 is the plain patch bit for bit). SurfaceBlend and Patch.crown are noted under format 22.

crates/doc/src/walk.rs

@@ -44,6 +44,7 @@ impl Walk for ProfileSel {}
 impl Walk for solidcraft_sketch::Sketch {}
 impl Walk for solidcraft_kernel::StepNode {}
 impl Walk for crate::document::Operation {}
+impl Walk for solidcraft_kernel::Continuity {}
 impl Walk for crate::document::Direction {}
 impl Walk for crate::document::FilletFit {}
 impl Walk for crate::document::MeshData {}
@@ -136,6 +137,36 @@ impl<T> Each<T> for Vec<T> {
     }
 }
 
+impl<T, const N: usize> Each<T> for [T; N] {
+    fn each<'a>(&'a self, f: &mut dyn FnMut(&'a T)) {
+        for t in self {
+            f(t)
+        }
+    }
+    fn each_mut<'a>(&'a mut self, f: &mut dyn FnMut(&'a mut T)) {
+        for t in self {
+            f(t)
+        }
+    }
+}
+
+impl<T, const N: usize> Each<T> for Option<[T; N]> {
+    fn each<'a>(&'a self, f: &mut dyn FnMut(&'a T)) {
+        if let Some(a) = self {
+            for t in a {
+                f(t)
+            }
+        }
+    }
+    fn each_mut<'a>(&'a mut self, f: &mut dyn FnMut(&'a mut T)) {
+        if let Some(a) = self {
+            for t in a {
+                f(t)
+            }
+        }
+    }
+}
+
 impl<T> Each<T> for Option<Vec<T>> {
     fn each<'a>(&'a self, f: &mut dyn FnMut(&'a T)) {
         for t in self.iter().flatten() {