Avoid extra cloning on scene impls

[eckz]

Objective

• Some code inside the scene.rs contained unnecessary .clone() calls. Most probably because Scene::resolve was not consuming itself before.
• I'm not sure if this improves anything, as the compiler might be intelligent enough to remove this calls already, but I don't see any drawbacks either.

Solution

• Remove the .clone() calls when not necessary.

Testing

• Local unit tests