chore: refactoring and cleanup for Gizmo

thermion_dart/native/src/GridOverlay.cpp

@@ -11,7 +11,7 @@
 #include "SceneManager.hpp"
 #include "Log.hpp"
 
-namespace thermion_filament {
+namespace thermion {
 
 using namespace filament::gltfio;
 
@@ -194,4 +194,4 @@ void GridOverlay::destroy()
     _engine.destroy(_gridEntity);
 }
 
-} // namespace thermion_filament
+} // namespace thermion