Support Color in the Python adapter generator; map Leader.override_color

Color converts as {'kind': ByLayer|None|ByBlock|Index|Rgb, 'value': ...}.
Leader.override_color is now writable; neither DWG nor DXF stores it, which
is recorded as a fourth persistence blocker with a canary assertion.

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

crates/ocs_plugin_api/build.rs

@@ -778,6 +778,7 @@ fn generate_entity_coverage(out_dir: &Path, registry: &TypeRegistry) {
                             | "text_height"
                             | "text_width"
                             | "vertices"
+                            | "override_color"
                             | "annotation_handle"
                             | "normal"
                             | "horizontal_direction"