Add pedersen commitments to leaf commitments instead of only Poseidon

[drewstone]

We should test out pedersen commitments to (r, nullifier) as well as our current Poseidon(r, nullifier). This would potentially present some speedups on the front-end and could be more optimised for the leaf commitments.

For the front-end, we wouldn't need to instantiate the Poseidon parameters to generate deposit notes. Instead, we could simple compute a pedersen hash from the base field generator and the random elements (r, nullifier) sampled from the field.

[drewstone]

more constraints than Poseidon