fix: resolve verifier slashing bypass via exit cooldown

[Yasir-TechGuy]

Closes #181

Overview

This PR resolves issue #181 (VerifierSlashing bypass via exit) by mitigating a critical vulnerability where a malicious verifier could front-run an incoming slash transaction by calling withdrawStake to instantly remove their funds.

🎯 Changes Implemented

1. Updated Data Structures*: Added an exitTime timestamp field to the VerifierStake struct in TruthBountyWeighted.sol to record when an exit process is initiated.
2. Enforced Timelock Cooldown: Refactored the withdrawStake function to require a 2-day cooldown period. When first called, it commits an exitTime checkpoint and halts execution. Funds can only be successfully transferred out after the 2-day delay has fully elapsed.
3. Protected Slashing Mechanism: By delaying token withdrawals, verifier funds are safely locked inside the contract for 2 days, guaranteeing that an admin's slash transaction has ample time to land if a violation occurred.

✅ Verification

• Solved compilation errors and verified that TruthBountyWeighted.sol builds successfully.
• Implemented logic in adherence to protocol security invariants to completely eliminate the front-running exit vector.

[dDevAhmed]

@Yasir-TechGuy update branch

[Yasir-TechGuy]

nice woking with u