Modify high-level Jolt SDK to allow preprocessing to be de/serialized and performed separately for prover/verifier

This PR implements the changes to the high-level Jolt API described in #585. The main features are as follows:

• Separate steps for compilation of the guest program, preprocessing, and proving/verifying
• Separate preprocessing types and generated functions for the prover and verifier
• Implement CanonicalSerialize and CanonicalDeserialize for preprocessing, along with helper functions to save/read it in the target directory
• Remove input/output from the proof and make verify take it as an argument directly (as discussed in the issue)

A couple of other points to mention:

• Implementing CanonicalSerialize and CanonicalDeserialize on the preprocessing involved making a PR to ark-algebra to provide implementations of these for signed integers. That work will probably need to be merged into https://github.com/a16z/arkworks-algebra/ before this can be merged. I'll go ahead and make a PR for that. The arkworks PR is here: Implement CanonicalSerialize and CanonicalDeserialize for signed integers arkworks-rs/algebra#953
• This PR separates the prover and verifier preprocessing, but it doesn't currently try to pare the verifier's preprocessing down to the minimum necessary. I wasn't sure how deep to go there, so it seemed best to limit the scope of this PR to API changes, and leave the latter for a separate PR.

Closes #585