Support texture streaming on CPU in Cycles using .tx files

Cycles should support texture streaming on the CPU by making use of .tx files and OpenImageIO. This would allow only the necessary mip levels to be loaded at render time, reducing memory usage for heavy texture scenes like scans or large environments.

This suggestion is only for CPU rendering for now. Cycles already uses OpenImageIO on CPU, and .tx mipmaps and tiles can be loaded on demand with relatively little development work.

GPU texture streaming is a much bigger project and would require different implementations for CUDA, HIP, Metal, etc. That’s outside the scope of this request.

This would be a practical first step toward more efficient texture handling in Cycles, and could make a big difference on most renders but especially systems with limited RAM.