feat(multisig): add timelock mechanism and TransactionData struct with NatSpec documentation

[SynnekOG]

Summary

This PR enhances MultiSigContractV2 with a timelock mechanism for critical operations and introduces a structured representation of transaction metadata via the new TransactionData struct. These additions improve contract security, governance transparency, and maintainability.

Changes

• Timelock Mechanism

  • Added uint256 public timelockDelay = TIMELOCK_DURATION;
  • Ensures sensitive operations are subject to a delay, preventing immediate execution and allowing stakeholders time to react.
  • Fully documented with NatSpec comments.

• New Struct: TransactionData

  • Encapsulates full metadata for multisig transactions:
    • txId: Unique transaction identifier.
    • owner: Initiator of the transaction.
    • signers: Set of eligible signers.
    • signatures: Collected approvals.
    • requiredSignatures: Threshold for execution.
    • createdAt: Timestamp when the transaction was created.
    • expiresAt: Timestamp for expiration.
    • executedAt: Timestamp for successful execution.
    • executed: Boolean flag for execution status.
    • cancelled: Boolean flag for cancellation status.
    • description: Human-readable description of the transaction.
    • data: Encoded calldata for execution.
    • timelockEnd: Enforces minimum waiting period before execution.

• Formatting

  • Ran forge fmt for style consistency.

• Codebase Metrics

  • 21 additions
  • 0 deletions

Why This Change

• Introduces delayed execution security (timelock), a critical safeguard against rushed or malicious governance actions.
• Provides a rich transaction data model (TransactionData) to support advanced governance features such as auditing, expiration, cancellation, and historical queries.
• Improves readability and auditability of the contract with NatSpec-compliant documentation.

Impact

• Security: Strengthens governance safety with enforced waiting periods.
• Transparency: Stakeholders gain visibility into transaction lifecycle metadata.
• Extensibility: Lays the foundation for features like transaction queuing, cancellation, and UI-friendly dashboards.
• No breaking changes for existing deployments (new features are additive).

Testing

• Verified compilation with new state variable and struct.
• Pending unit tests for:
  • Enforcement of timelock delay before execution.
  • Proper lifecycle transitions in TransactionData.
  • Edge cases (expiry, cancellation, insufficient signatures).

Next Steps

• Implement transaction queuing and execution logic using TransactionData.
• Add events for timelock start, expiry, and execution.
• Write Foundry tests covering timelock behavior and transaction metadata accuracy.