feat: robust secret sharing (RSS)

[lonerapier]

Allow reconstruction even with some forged or corrupted shares, detecting and rejecting invalid ones.

Approach

• Extend feat: verifiable secret sharing (VSS) #7 to detect and identify inconsistent shares.
• Add MAC/tag to each share based on secret polynomial commitments.
• Expose API:

fn recover_robust(shares: &[Share], commitments: &Commitments)
    -> Result<Secret, Vec<CorruptedShare>>;

Tasks

• Implement cheater detection/identification logic.
• Integrate with existing VSS commitments.
• Benchmark overhead of verification.

References

• Rabin & Ben-Or, “Verifiable Secret Sharing and Multiparty Protocols with Honest Majority” — PDF