set_local_scale does not take a Vec3

`SceneNode3d::local_scale()` returns a `Vec3` but `SceneNode3d::set_local_scale()` takes 3 `f32`s. It would make copying scales easier if `set_local_scale()` also took a `Vec3`. Other node properties like `rotation()`/`set_rotation()` and `position()`/`set_position()` already use the same types for getter and setter and `set_local_scale()` internally constructs a `Vec3` anyway.

Start at the SceneNode3d::local_scale() and SceneNode3d::set_local_scale() entry points, then compare them with the existing rotation() / set_rotation() and position() / set_position() pairs. Update the setter interface so it accepts the same Vec3 type returned by the getter, while preserving the existing scale behavior. Done means scale values can be copied directly between SceneNode3d nodes and the project checks pass.

Written by the indexing model from the issue text.