Draft: Halo integration (first steps)

• Implementation of the Inner-Product Argument (IPA) commitment scheme
• Unified treatment of KZG and IPA through the notion of Homomorphic Polynomial Commitment (HPC)
• Functor from HPC to Polynomial Commitment Scheme (PCS), the signature that Plonk expects
• General Fr (not hardcoded for Bls): automated generation of roots of unity and quadratic non-residues

IPA uses Pallas instead of Bls.

Main TODO task:

• Implement the accumulator scheme for IPA