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 <noreply@anthropic.com>

src/scene/mod.rs

@@ -7504,7 +7504,7 @@ impl Scene {
             let Some(EntityType::Viewport(viewport)) = self.document.get_entity(handle) else {
                 continue;
             };
-            if viewport.common.owner_handle != paper_block || !viewport.status.is_on {
+            if viewport.common.owner_handle != paper_block || !viewport.is_on() {
                 continue;
             }
             let mode = render_mode_override.unwrap_or(viewport.render_mode);