Upgrade `single`.rs to zexe compatible `EngineBLS` about bls HOT 8 CLOSED

trait .. {
    ..

    /// Prepare public key for Miller loop
    fn prepare_public_key(g: impl Into<Self::PublicKeyGroupAffine>) -> Self::PublicKeyPrepared {
        let g1: Self::PublicKeyGroupAffine = g.into();
        Self::PublicKeyPrepared::from(g1)
    }

    /// Prepare signature for Miller loop
    fn prepare_signature(g: impl Into<Self::SignatureGroupAffine>) -> Self::SignaturePrepared {
        let g2: Self::SignatureGroupAffine = g.into();
        Self::SignaturePrepared::from(g2)
    }
}

    fn prepare_public_key(g: impl Into<Self::PublicKeyGroupAffine>) -> Self::PublicKeyPrepared {
        prepare_g1(g)
    }

error[E0284]: type annotations needed: cannot satisfy `<_ as PairingEngine>::G1Affine == <E as PairingEngine>::G1Affine`
   --> src/engine.rs:256:9
    |
256 |         prepare_g1(g)
    |         ^^^^^^^^^^ cannot satisfy `<_ as PairingEngine>::G1Affine == <E as PairingEngine>::G1Affine`

    fn prepare_public_key(g: impl Into<Self::PublicKeyGroupAffine>) -> Self::PublicKeyPrepared {
        prepare_g1::<E>(g)
    }

    error[E0599]: no function or associated item named `prepare_g1` found for type parameter `E` in the current scope
   --> src/engine.rs:256:12
    |
256 |         E::prepare_g1(g)
    |            ^^^^^^^^^^ function or associated item not found in `E`