Add sponge helper to take ref bytes as argument

[vlopes11]

Describe what you want implemented Need a function that will convert arbitrary slices of bytes into a BlsScalar

Describe "Why" this is needed We are limited by scalars when actually anything could be hashed by poseidon, having the proper implementation available.

Describe alternatives you've considered Duplicating code everywhere with different scalar aggregator strategies that might lead to inconsistencies between libraries.

Additional context We need to perform a hash of the contract id and transaction in the hosted environment of rusk-vm to calculate the transaction hash: https://github.com/dusk-network/rusk/issues/402