Add transfer_with_attestation nonce and expiry to prevent attestation replay

[greatest0fallt1me]

Description

Attested transfers must include a nonce and an expiry timestamp so an attestation cannot be replayed. Nonces are per-signer and monotonically consumed.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/test_transfer_with_attestation.rs
• Consumed nonces persist to reject reuse

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/attestation-nonce-expiry
• Implement changes
  • Extend attestation struct with nonce, expires_at
  • Persist consumed set keyed by (signer, nonce)
  • Reject expired or replayed attestations
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Attestation used at exact expiry second
• Include test output and security notes

Example commit message

feat: add nonce and expiry to transfer attestations

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[devv-leo]

@devv-leo has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I’ll get this resolved in 24 hours if assigned to me.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@devv-leo's PR #701 was approved and merged by @thlpkee20-wq.

🏆 @devv-leo: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (118 total points). Track your full progress on GrantFox.

👏 Great work, @devv-leo! Keep contributing to RevoraOrg.

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This issue has been completed by @devv-leo as part of the Stellar Wave Program's 7th Wave 🥳

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