Add low-risk NVENC encoding option to ImageTransitionNode, VideoImageOverlay,
and VideoSplitterNode. Each node now includes a use_gpu parameter (default: False)
that enables hevc_nvenc when available, with automatic fallback to libx264 if
NVIDIA GPU is unavailable or NVENC fails.
Changes:
- ImageTransitionNode: Add use_gpu parameter for MP4 frame encoding
- VideoImageOverlay: Add use_gpu parameter for overlay video encoding
- VideoSplitterNode: Add use_gpu parameter for segment encoding
Expected gains: 5-10x speedup for GPU users (hevc_nvenc vs libx264)
Risk level: VERY LOW (zero breaking changes, backward compatible)
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>