prioritize missing optix features

[brendancol]

Missing Stable OptiX Features:

1. Barycentric Coordinates (u, v) - OptiX provides these via optixGetTriangleBarycentrics(). Essential for:
   - Texture/attribute interpolation on terrain
   - Precise hit point calculation
   - Draping imagery onto terrain
2. Ray Flags - Currently hardcoded to OPTIX_RAY_FLAG_NONE. Exposing these would enable:
   - TERMINATE_ON_FIRST_HIT - Much faster shadow/occlusion queries (binary yes/no)
   - CULL_BACK_FACING_TRIANGLES - Skip backfaces for closed meshes
   - DISABLE_ANYHIT - Already implicitly done, but explicit control is useful
3. Any-Hit Shaders - Currently disabled. Would enable:
   - Transparency/alpha cutout (vegetation, fences)
   - Counting all intersections along a ray
   - Custom acceptance criteria
4. Multiple Ray Types - Currently single ray type. Separate types for:
   - Primary rays vs shadow rays (different SBT entries)
   - Different payload sizes per ray type