Arkworks upgrades

[burdges]

We should upgrade this code to the latest arkworks. It's possible this cannot be done right away, as some of our other arkworks dependencies might not yet be upgraded either.

It should be orthogonal whether the host is upgraded or not, but we should watch for things that break. We use non-cannonical serialization of projective points here, which becomes our maintanance problem if arkworks ever changes their internal projective representation. We could replace projective serialization by affine at some small performance cost, if we wished to avoid that risk.

Anyways this is probably not something to rush on, but just fyi..