Map SectionSymbol, the last unmapped kind

points is canonical; the host derives the point counts and refreshes the
end/tick/label projections with sync_display_fields when it changes, and
validates that style and view-representation references are existing class
objects. The lifecycle test passes every gate in DWG; DXF reopens the symbol
as an unknown entity because cadcodec dispatches SECTIONLINE only inside
blocks (pinned by a canary and already in the cadcodec write-up).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugins/opencad-python/src/ocs_module.rs

@@ -4983,7 +4983,7 @@ mod tests {
                 );
             }
         }
-        assert_eq!(emitted.len(), 42);
+        assert_eq!(emitted.len(), 43);
     }
 
     #[cfg(feature = "experimental-host-model")]