feat(rust): Add workspace deps, tests, and refine training modules
- Cargo.toml: Add wifi-densepose-train to workspace members; add
petgraph, ndarray-npy, walkdir, sha2, csv, indicatif, clap to
workspace dependencies
- error.rs: Slim down to focused error types (TrainError, DatasetError)
- lib.rs: Wire up all module re-exports correctly
- losses.rs: Add generate_gaussian_heatmaps implementation
- tests/test_config.rs: Deterministic config roundtrip and validation tests
https://claude.ai/code/session_01BSBAQJ34SLkiJy4A8SoiL4
2c5ca308a4