Class-A surfacing 3/3: blend curves, curved-edge fillets, the G2 corner and continuity analysis (#1642)

Thanks @midasdf.

crates/io/src/lib.rs

@@ -864,6 +864,7 @@ mod tests {
                 body: None,
                 style: Default::default(),
                 fit: Default::default(),
+                corner: Default::default(),
             },
             None,
         )
@@ -948,6 +949,7 @@ mod tests {
                 body: None,
                 style: Default::default(),
                 fit: Default::default(),
+                corner: Default::default(),
             },
             None,
         )