Verify a Groth16 proof using the stored verification key.
fn verify(
env: soroban_sdk::Env,
proof: Groth16Proof,
public_inputs: soroban_sdk::Vec,
) -> Result Constructor: initialize the contract with a verification key.
fn __constructor(
env: soroban_sdk::Env,
vk: VerificationKeyBytes,
) -> Result<(), Groth16Error>