review(#1660, #1663): associative sweep scan, arc angles, viewport off bit

- refresh_associative_sweeps runs on every edit and scanned the xdata of
  every entity; it now returns at once when no associative swept surface
  exists (its application is not registered) and looks at surfaces only.
- An arc's end angle was raised by TAU in a loop, which never ends on a
  huge angle from a damaged file; the sweep is taken with rem_euclid.
- The sweep DELOBJ test expected surface sweeps to delete their sources,
  which #1663 changed on purpose: an associative surface keeps them.
- codec c9ffcac (opencadcodec #103) adds an explicit viewport-off bit: the
  viewport on state is read with is_on() and set with turn_on()/turn_off()
  everywhere, so a viewport the file marks off shows off and can be turned
  back on from Properties.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/scene/mspace.rs

@@ -801,7 +801,7 @@ impl Scene {
                 let Some(EntityType::Viewport(vp)) = self.document.get_entity(*handle) else {
                     return None;
                 };
-                if !vp.status.is_on {
+                if !vp.is_on() {
                     return None;
                 }
                 let rect = self.viewport_screen_rect(vp.common.handle, canvas)?;
@@ -838,7 +838,7 @@ impl Scene {
     pub fn viewport_displays_content(&self, vp_handle: Handle) -> bool {
         matches!(
             self.document.get_entity(vp_handle),
-            Some(EntityType::Viewport(vp)) if vp.status.is_on
+            Some(EntityType::Viewport(vp)) if vp.is_on()
         )
     }
 
@@ -850,7 +850,7 @@ impl Scene {
             let Some(EntityType::Viewport(vp)) = self.document.get_entity(*handle) else {
                 return None;
             };
-            if vp.status.is_on {
+            if vp.is_on() {
                 Some(vp.common.handle)
             } else {
                 None