Function decrypt_file_with_cache 

pub fn decrypt_file_with_cache(
    path: &Path,
    key_cache: &DashMap<[u8; 16], Arc<OnceLock<Result<Zeroizing<[u8; 32]>, String>>>>,
    cache: Option<(&SaltCacheSender, &[u8])>,
    master_key: &[u8],
) -> Result<()>

Decrypt a single file using streaming chunked decryption, with a thread-safe cache for derived keys and an optional cache sender for deterministic re-encryption.

The cache tuple contains (sender, relative_key) — the caller is responsible for computing the repo-relative path key.