Expose transform controls (rotation & scale) for video-generated Tilesets in Cesium for Unity

### Feature

I’m working with Tilesets generated from video and I find that, in the current Cesium for Unity API, there is no way to apply a custom rotation or non-uniform scale to the loaded tileset model itself. This limits my ability to align or adjust the model in the scene, especially when the source imagery is not perfectly aligned to axis, or when I want to locally tweak its orientation/size.

In the Cesium3DTileset documentation it is recommended that “the Transform of the GameObject that contains this component, and its ancestors, should be an identity transform: 0 position, 0 rotation, 1 scale” to avoid misalignment with other globe tilesets. However, this also means users are discouraged (or prevented) from applying arbitrary transforms to the tileset.

I’d also mention that applying a local transform change to a tileset fundamentally breaks the display of the tileset — tiles begin to misalign, disappear, or fail to load properly. This makes it impossible to use any Unity-native transform tools to rotate or scale the model, even for small local corrections.

To me, it would be very useful if the API allowed a controlled override or extension point to apply a model transform matrix (rotation, scale, translation) on top of the georeference mapping, or optionally switch the tileset into a “local space” mode where it can be manipulated like a normal 3D model.