Function build_native_cdylib_cached 

pub fn build_native_cdylib_cached(
    rust_source: &str,
    fn_name: &str,
    cache_dir: &Path,
) -> Result<PathBuf, String>

build_native_cdylib with a persistent cache (HOTSWAP §Axis-3 / P16). The artifact lives at cache_dir/aot_<fn>_<key>/… keyed by aot_cache_key; an identical function reuses its .so across runs (no rebuild), and a toolchain change yields a new key so the stale library is never loaded.