Is your feature request related to a problem? Please describe.
The PR #2915 is adding foundations for the scene hierarchy with an imgui widget to view it and change parts visibility.
It's necessary to have a libf3d API so libf3d based apps can also display the scene hierarchy in another UI framework.

Describe the solution you'd like
The API has to be discussed first but it could look like:

scene& visitSceneHierarchy(const std::function<void(int, int, const std::string&)>& callback) const; scene& setNodeVisibility(int nodeIndex, bool visible) const;

And the caller can call it like that:

scene.visitSceneHierarchy([](int nodeIndex, int parentIndex, const std::string& label) { // render scene hierarchy });

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

Contribution
Please tell us if you are able to contribute (Can you develop this new feature?)
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