Function verify_pack_tarball 

pub fn verify_pack_tarball(
    pubkey_hex: &str,
    tarball_bytes: &[u8],
    sig_bytes: &[u8],
) -> Result<(), SigError>

Verify a policy-pack tarball signature using the empirically-discovered scheme: Ed25519 over sha256(tarball_bytes).

pubkey_hex is the issuer’s raw 32-byte Ed25519 public key, hex-encoded (64 chars). tarball_bytes is the verbatim .tar.gz contents. sig_bytes is the 64-byte raw signature read from <ver>.sig.