Refactor Hyrax Batching

[sragss]

Includes a batch_size param in calls to CommitmentScheme::{batch_commit, batch_prove} and includes the batch_size param in the CommitmentScheme::BatchedProof struct if needed.

Two unfortunate things:

• Leaky abstraction: Hyrax is the only commitment scheme we know about that needs the batch_size param to be used as the Hyrax sizing ratio. Theoretically this could be refactored to be an associated type on CommitmentScheme called BatchCommitConfig which could store other info, we just aren't aware of another commitment scheme that needs it.
• Bad parameter naming: batch_size isn't quite the correct parameter name. Currently we call CommitmentScheme::{batch_commit, batch_prove} for a range of real batch sizes {163, 40}. Across all of these NUM_R1CS_POLYS=64 is close enough to get desired performance. Also batch_prove is often passed a subset of the batch's polynomials, but still needs the matching batch_size param to whatever was committed. We could return to RATIO but only makes sense in the context of Hyrax.

[sragss]

Currently batch_commit is called from impl StructuredOpeningProof for {Bytecode, RAM, InstructionLookups} / VM::Commit / R1CSProof::compute_witness_commit.

StructuredOpeningProof is not used anymore for Read/Write across {Bytecode, RAM, InstructionLookups} in favor of VM::commit. It is still used for Init / Final but these have a batch_size / RATIO of 1.

R1CSProof::compute_witness_commit should likely be refactored to R1CSProof::compute_witness and VM::commit should handle the batch commitment.

A decent solution would be to switch the batch_size param to an enum CS::BigBatch / CS::SmallBatch which for Hyrax would correspond to NUM_R1CS_POLYS / 1.