Add Gower Express - Fastest GPU-accelerated Gower Distance Implementation

[momonga-ml]

Summary

• Added Gower Express to the Python General-Purpose Machine Learning section
• GPU-accelerated similarity matching library for mixed data types
• 15-25% faster than alternatives with production-ready reliability
• Perfect for clustering, recommendation systems, and ML pipelines

Test plan

• Added entry in correct alphabetical position (after gensim)
• Followed existing format and style conventions
• Verified link and description accuracy