feat(vault): add permissionless vault unlock operation

[coderDom-x]

Summary

This PR introduces a permissionless unlock_vault operation that allows anyone to unlock a vault once it reaches its maturity timestamp, enabling users and indexers to observe vault maturity without requiring a withdrawal.

Changes

• Added a new unlock_vault operation to the vault contract.
• Ensured the operation only succeeds after the configured unlock timestamp.
• Implemented a one-time state transition from Locked to Unlocked.
• Emitted the documented vault unlock event upon successful unlock.
• Preserved vault ownership, balances, and asset configuration during unlock.
• Updated shared types, errors, events, and utilities where required.
• Added unit tests covering unlock behaviour before, at, and after the maturity timestamp.
• Updated the contract README with the new operation and expected behaviour.

Testing

• Verified unlocking before the maturity timestamp fails.
• Verified unlocking at the maturity timestamp succeeds.
• Verified unlocking after maturity succeeds.
• Confirmed the vault transitions from Locked to Unlocked exactly once.
• Verified the unlock event is emitted.
• Confirmed ownership, balances, and asset configuration remain unchanged.

Closes #82