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/app/command_driver/tests.rs

@@ -935,14 +935,17 @@ mod delobj_tests {
                 expected,
             );
         }
-        assert_eq!(
-            sweep_source_presence(2, crate::command::ExtrudeMode::Surface),
-            (false, false),
-        );
-        assert_eq!(
-            sweep_source_presence(3, crate::command::ExtrudeMode::Surface),
-            (false, true),
-        );
+        // A swept surface is associative by default (SURFACEASSOCIATIVITY 1)
+        // and keeps the profile and path it follows, whatever DELOBJ says;
+        // DELOBJ reaches surfaces only with associativity off, a profile-wide
+        // switch this parallel test leaves alone.
+        assert!(crate::scene::model::sweep_model::surface_associativity());
+        for value in [2, 3] {
+            assert_eq!(
+                sweep_source_presence(value, crate::command::ExtrudeMode::Surface),
+                (true, true),
+            );
+        }
     }
 }