Rust Code Quality and Website Improvements for Apache Mahout

Apache Mahout's QDP is a GPU-accelerated quantum state encoding library bridging Rust, CUDA, and Python — yet its contributor experience lags behind its technical ambitions: unsafe blocks lack // SAFETY: justifications, public APIs are undocumented, Clippy warnings accumulate, and neither cargo doc nor Python API generation is enforced in CI. This project tackles all three layers in 12 weeks. Phase 1 narrows unsafe blocks with proper safety documentation, achieves 100% RFC 505-compliant API coverage, eliminates all Clippy warnings, and adds ≥25 GPU-independent unit tests. Phase 2 builds an automated Sphinx pipeline for the Python (qumat/) API and validates Rust ↔ Python interface consistency. Phase 3 fixes broken links on the Docusaurus site and integrates both cargo doc and Python doc generation into CI. Key deliverables: refactored unsafe blocks across 4 core files, 100% Rust API doc coverage, zero Clippy warnings, ≥25 new unit tests, automated Python API docs, a rustdoc.yml CI workflow, and a contributor documentation guide — creating a unified, drift-resistant documentation experience across QDP's Rust and Python interfaces.