- Add SystemFunctionCache with SystemFunctionBackend trait for per-tenant
  feature flag caching, mirroring the TenantCache pattern
- Add PyO3 Python bindings (feature-gated behind "python" feature) exposing
  TenantCache, SystemFunctionCache, CacheConfig, TenantInfo, and
  SystemFunctions to Python with async support via pyo3-async-runtimes
- Add pyproject.toml for maturin-based wheel builds
- Add GitHub Actions workflow for building and publishing wheels to
  Google Artifact Registry

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>