OptiX 9.1, CUDA 13.2

• Moved to OptiX 9.1, recompliled with CUDA 13.2 (note: minimal requirements are now driver r590 and compute capability 7.5).
• Improved/simplified callbacks logic: rt_completed is now executed only after the last accumulation frame instead of every accumulation frame. Also, the video encoder adds frame to the output clip on the "accumulation done" signal instead of "launch finished". This allows for using all the work balancing modes in animation workflows, while it is still possible to configure min_accumulation_step == max_accumulation_frames to get the same behavior as before.
• Added function to get current noise level (value updated after each accumulation frame).