security: reject replayed MiningProof nonces

[createkr]

Summary

This change hardens Proof of Antiquity validation by rejecting replayed MiningProof nonces across block boundaries.

What changed

• Added per-wallet nonce tracking in ProofOfAntiquity
• Rejected reused nonces in submit_proof() with a dedicated NonceReuse error
• Preserved nonce history across block resets so the same nonce cannot be replayed in a later block
• Added focused tests covering nonce replay rejection and cross-block persistence

Why

The previous implementation accepted proofs without checking whether a wallet had already used the supplied nonce. Because pending proof state is cleared between blocks, the same proof nonce could be replayed in later blocks and accepted again.

Scope

• rips/src/proof_of_antiquity.rs only

Closes #2057

Payout Wallet

RTC1d48d848a5aa5ecf2c5f01aa5fb64837daaf2f35