Hi, calling all generics wizards, that might be able to understand rustcryptos generics magic?!
I am trying to express a generics bound that allows me to express a signer that works for both ecdsa and rsa.

I have this currently, and that works great for all ecdsa curves, but is it possible to somehow expand that to also allow RSA and possibly also eddsa?

```rust

#[derive(Debug)]
pub struct Signature<T: PrimeCurve>
where
    SignatureSize<T>: core::ops::Add<ecdsa::der::MaxOverhead> + ArrayLength<u8>,
    ecdsa::der::MaxSize<T>: ArrayLength<u8>,
{
    signature: ecdsa::der::Signature<T>,
}

pub struct Signer<'a, T: PrimeCurve, RNG: CryptoRngCore> {
    pub secret_key: SecretKey<T>,
    pub scheme: SignatureScheme,
    pub rng: &'a mut RNG,
}

impl<'a, T: PrimeCurve, RNG: CryptoRngCore> Signer<'a, T, RNG>
where
    SignatureSize<T>: core::ops::Add<ecdsa::der::MaxOverhead> + ArrayLength<u8>,
    ecdsa::der::MaxSize<T>: ArrayLength<u8>,
{
    pub fn sign(&mut self, message: &[u8]) -> Signature<T>
    where
        T: CurveArithmetic + DigestPrimitive,
        <T as CurveArithmetic>::Scalar: SignPrimitive<T>,
    {
        let signing_key = SigningKey::from(&self.secret_key);
        let signature = signing_key.sign_with_rng(self.rng, &message);

        Signature { signature }
    }

    pub fn signature_scheme(&self) -> SignatureScheme {
        self.scheme
    }
}

```