Unify the Sponge types.

[rot256]

There are multiple sponge types, i.e. in "Kimchi":

pub trait FrSponge<Fr: Field> {
    /// Creates a new Fr-Sponge.
    fn new(p: ArithmeticSpongeParams<Fr>) -> Self;

    /// Absorbs the field element into the sponge.
    fn absorb(&mut self, x: &Fr);

    /// Creates a [ScalarChallenge] by squeezing the sponge.
    fn challenge(&mut self) -> ScalarChallenge<Fr>;

    /// Absorbs the given evaluations into the sponge.
    // TODO: IMO this function should be inlined in prover/verifier
    fn absorb_evaluations(&mut self, p: &[Fr], e: &ProofEvaluations<Vec<Fr>>);
}

And in "Oracles":

impl<P: SWModelParameters, SC: SpongeConstants>
    FqSponge<P::BaseField, GroupAffine<P>, P::ScalarField> for DefaultFqSponge<P, SC>
where
    P::BaseField: PrimeField,
    <P::BaseField as PrimeField>::BigInt: Into<<P::ScalarField as PrimeField>::BigInt>,
{
    fn new(params: ArithmeticSpongeParams<P::BaseField>) -> DefaultFqSponge<P, SC> {
        ...   
    }

    fn absorb_g(&mut self, g: &[GroupAffine<P>]) {
        ...
    }

    fn absorb_fr(&mut self, x: &[P::ScalarField]) {
        ...
    }

    fn digest(mut self) -> P::ScalarField {
        ...
    }

    fn challenge(&mut self) -> P::ScalarField {
        self.squeeze(CHALLENGE_LENGTH_IN_LIMBS)
    }

    fn challenge_fq(&mut self) -> P::BaseField {
        self.squeeze_field()
    }
}

I believe these can be unified, particularly after adopting #636 (Introduce Absorb/Challenge traits) which enables implementing/deriving Absorb for ProofEvaluations (as done in the rust version of pickles)

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