feat: Serialize proofs

[sragss]

The strategy is to use ark_serialize::{CanonicalSerialize, CanonicalDeserialize} recursively as low as possible via macros. If we'd like to expose serde::Serialize we should do this at the highest level. If we try to do serde at a lower level we'll have to use serde's serialize_with on nearly every field.

The lack of compatibility between these two appears contentious:

• What is the difference between ark-serliaze and serde ? arkworks-rs/algebra#178
• add serde to Field arkworks-rs/algebra#506
• [meta] consistent serde strategy  EspressoSystems/jellyfish#288

Issues remaining:

• Does not yet remove generators
• R1CS proof contains the UniformSpartanKey which should not be in the proof, but rather "known" by the verifier

[sragss]

The PR manually implements ark_serialize::{CanonicalSerialize, CanonicalDeserialize} for types including PhantomData<T>. I believe the macros will work for these as long as T: Send + Sync based on the arkworks default impls.

[sragss]

T: Send + Sync strategy described above works.