Enhancement: Audio Stem Separation for Windows (Cross-Platform Parity with macOS HTDemucs/CoreML

[bravado67]

Is your feature request related to a problem?:
The new audio stem separation feature (HTDemucs via CoreML) is currently limited to M Series Macs and iPad. Windows users — who represent the majority of the xLights community — have no access to this functionality. Third-party tools like Moises.ai are currently the only viable option for Windows users needing stem separation for timing creation.

Describe the solution you'd like:
A Windows-compatible implementation of audio stem separation using an appropriate cross-platform framework such as ONNX Runtime or DirectML, allowing Windows users to separate drums, bass, vocals, and other stems directly within xLights without third-party software.

Alternatives considered:
Moises.ai — works well but requires leaving xLights and lacks native integration with timing tracks
VAMP plugins — do not provide stem separation
ONNX Runtime — open source, cross-platform, supports the same HTDemucs models and may be the most viable path for Windows implementation

Additional context:
I discussed this directly with Dan Kulp who confirmed that CoreML made this straightforward on Apple Silicon but acknowledged no equivalent exists natively on Windows and that further research would be needed. This feature has significant community demand — stem-based timing creation is a major workflow improvement for sequencers at all levels.