Map RasterImage with host-created image definitions

Scripts name an image file; the host reads its pixel size, creates and links
the ImageDefinition and derives size and the default clip boundary.
staged_python_raster_image_lifecycle_over_real_ipc passes every gate in OCS
with a real PNG. ACAD_IMAGE_DICT and reactor linkage are not created, so the
kind is recorded as integration-tested.

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

plugins/opencad-python/src/ocs_module.rs

@@ -4756,7 +4756,7 @@ mod tests {
                 );
             }
         }
-        assert_eq!(emitted.len(), 31);
+        assert_eq!(emitted.len(), 32);
     }
 
     #[cfg(feature = "experimental-host-model")]