Constraints for nimue

When using nimue in the context of recursive proofs, a notable sore point is that there is not a convenient way to implement the Fiat-Shamir in the recursive verifier circuit.
For comparison, the Sponge functionality in arkworks came with constraints associated ([here](https://github.com/arkworks-rs/crypto-primitives/blob/main/crypto-primitives/src/sponge/constraints/absorb.rs)).