Public inputs reconstruction: Switch to using Codecs

[iakovenkos]

Some classes like OpeningClaim are implementing their own reconstruct_from_public, those can be moved to Codecs or simplified

[ledwards2225]

The only thing doing this is currently OpeningClaim. I looked into resolving but I don't see any solutions that are actual simplifications. The problem is OpeningClaim is an outlier in terms of structure - we could build something that can handle generic structs but it would only apply to this one thing. Closing as a result