Make Groth16Error and PlonkError public

[srdtrk]

The verify functions which returns these errors are public, but the errors themselves are not. This makes handling these errors more difficult in external crates.

[puma314]

We moved the logic from this crate into the main sp1 repo and also significantly cleaned up the code: https://github.com/succinctlabs/sp1/tree/dev/crates/verifier

If you still have the same issue, can you file it as an issue in the SP1 repo?