fix(prover): use neutral error in verify_public_values

[esorense]

Motivation

verify_public_values is shared by both Plonk and Groth16 verification paths, but on failure it always returned Groth16VerificationError::InvalidPublicValues.

This caused error-type semantic leakage: a Plonk verification failure could be reported as a Groth16 error, which hurts observability and makes upstream error handling/debugging less reliable.

Solution

Use a protocol-neutral error in verify_public_values instead of hardcoding a Groth16-specific error.

What changed

• Added an internal neutral error type: PublicValuesVerificationError.
• Updated verify_public_values to return PublicValuesVerificationError::InvalidPublicValues on hash mismatch.
• Kept verification logic unchanged (SHA256/Blake3 dual-hash check is untouched).
• Kept scope minimal to crates/prover/src/verify.rs.

This preserves behavior while fixing error semantics so shared validation code no longer encodes Groth16-specific context.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

unknown contribution to verifier