dev: improve poseidon API

[tdelabro]

crates/starknet-types-core/src/hash/poseidon.rs

So the poseidon hash is defined this way.

And our API is this way:

impl StarkHash for Poseidon {
    /// Computes the Poseidon hash of two Felts, as defined
    /// in <https://docs.starknet.io/documentation/architecture_and_concepts/Hashing/hash-functions/#poseidon_hash.>
    fn hash(felt_0: &Felt, felt_1: &Felt) -> Felt {
        Felt(PoseidonCairoStark252::hash(&felt_0.0, &felt_1.0))
    }
    /// Computes the Poseidon hash of an array of Felts, as defined
    /// in <https://docs.starknet.io/documentation/architecture_and_concepts/Cryptography/hash-functions/#poseidon_array_hash.>
    fn hash_array(felts: &[Felt]) -> Felt {
        // Non-copy but less dangerous than transmute
        // https://doc.rust-lang.org/std/mem/fn.transmute.html#alternatives
        Felt(PoseidonCairoStark252::hash_many(unsafe {
            core::slice::from_raw_parts(
                felts.as_ptr() as *const FieldElement<Stark252PrimeField>,
                felts.len(),
            )
        }))
    }
}

impl Poseidon {
    /// Computes the Hades permutation over a mutable state of 3 Felts, as defined
    /// in <https://docs.starknet.io/documentation/architecture_and_concepts/Cryptography/hash-functions/#poseidon_array_hash>
    pub fn hades_permutation(state: &mut [Felt; 3]) {
        let mut state_inner = [state[0].0, state[1].0, state[2].0];
        PoseidonCairoStark252::hades_permutation(&mut state_inner);
        for i in 0..3 {
            state[i] = Felt(state_inner[i]);
        }
    }
}

This means that if you want to hash many elements you use hash_array, two elements you use hash. and for 1 single element you have to understand by yourselves that, according to poseidon specification, you must call hades_permutation(my_value, 0, 1).
As you can probably guess people don't know that and just do crazy things instead.

The inner labmdawork API is way more useful for developers: https://github.com/lambdaclass/lambdaworks/blob/7b5a638d4ce81f380ea5f43a22be41ef9b2d7ff2/crypto/src/hash/poseidon/mod.rs#L17

I would strongly recommend the addition of a hash_single method to the trait in order to make it more dev friendly

[varun-doshi]

I can take this one