feat: add model thumbnail rendering

[Lunarient]

Summary

This pull request adds 3D model thumbnail support for .obj, .gltf, .stl, .glb, and .fbx formats, using Open3D 0.19.0 for rendering. It supports textures and can color texture-less models. In the future, I plan to add a setting for users to choose their default model color.

This supersedes #693

This closes #351

Remaining Issues

The first issue with the pull request is that Open3D's OffscreenRenderer requires a dedicated thread, and it crashes if no thread adopts the renderer. I'm unsure how to integrate this with QThreads, so as a workaround, I set daemon=True for the rendering thread to prevent the software from hanging on exit. While this stops the hanging issue, it feels like a hacky solution.

The second issue is that sometimes on the first run the program seg faults, but on second run has no issues

Preview

Tasks Completed

• Platforms Tested:
  • Windows x86
  • Windows ARM
  • macOS x86
  • macOS ARM
  • Linux x86
  • Linux ARM
• Tested For:
  • Basic functionality
  • PyInstaller executable

[Lunarient]

Okay I'm no longer certain it's the model renderer that's causing the seg fault. I disabled the renderer and it still seg faults when adding new files to a library, but otherwise I don't know what causes it. If I someone else can test this, then it should be good to merge