feat: Add Additional Custom Errors for MultiSigContractV2

[SynnekOG]

Summary

This PR enhances MultiSigContractV2 with new custom error definitions to improve transaction validation, debugging clarity, and gas efficiency compared to traditional require strings. These errors provide precise failure reasons in multisignature transaction flows.

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Changes

src/MultiSigContractV2.sol

• Added 5 new custom errors:

  • MultiSigContract__NotSigned
    Thrown when a signer attempts to execute or finalize a transaction without having signed it.
  • MultiSigContract__InvalidTransaction
    Raised if the transaction does not meet validity checks (e.g., malformed or nonexistent).
  • MultiSigContract__TransactionExpired
    Ensures transactions past their expiration window cannot be executed.
  • MultiSigContract__TransactionNotReady
    Indicates an attempt to execute a transaction before required conditions (e.g., sufficient signatures) are met.
  • MultiSigContract__InvalidSignerCount
    Prevents execution if signer count is below quorum or exceeds allowable thresholds.

• Ran forge fmt to enforce consistent formatting.

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Motivation

• Improved Error Handling: Provides explicit, gas-efficient error reporting to users and developers.
• Transaction Safety: Ensures invalid, expired, or premature transactions cannot be executed.
• Governance Clarity: Custom errors clearly define failure modes, making multisig governance flows easier to audit and debug.

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Next Steps

• Integrate these errors into transaction lifecycle functions (propose, sign, execute).
• Expand test coverage to assert these errors are thrown under invalid conditions.
• Update Natspec documentation to reference new error semantics for auditors and integrators.

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