Turntable tool fails to generate turntable of an Arnold procedural

**To Reproduce**

Run the turntable tool on this scene: [procedural_turntable_test.zip](https://github.com/user-attachments/files/30315072/procedural_turntable_test.zip)

```
turntable --output turntable.usd --frames 30 --width 640 --height 360 --light-rig no_light procedural_turntable_test.usda
```

The tool does not recognize the procedural as a geometry and shows and empty scene warning.
```
turntable: bounding box of 'procedural_turntable_test.usda' is empty no renderable geometry found
```

Start by running the provided turntable command with procedural_turntable_test.usda from the attached scene and reproduce the empty-scene warning. Then trace the turntable tool's geometry recognition and bounding-box handling for Arnold procedurals. Done means the procedural is treated as renderable geometry and the command generates a non-empty turntable without the warning.

Written by the indexing model from the issue text.