feat: impl reentrancy guard and pause functionality

[Akshola00]

feat: impl reentrancy guard and pause functionality and security updates

closes #41

Summary

This pull request implements critical security and administrative features for the chainlib-contract project. The primary focus is on introducing a robust reentrancy guard to prevent reentrancy attacks and adding pause/unpause functionality for contract administrators to manage contract operations more securely.

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Detailed Description of Changes

1. Reentrancy Guard Implementation

• Introduced a reentrancy guard mechanism across relevant contract functions.
• Ensured that all sensitive or state-changing operations are protected against reentrancy attacks.
• Added modifiers and internal logic to ensure only one execution context per guarded function at a time.

2. Pause/Unpause Functionality

• Added the ability for contract administrators/owners to pause and unpause the contract.
• While paused, all critical contract functions (such as transfers, state changes, or sensitive operations) are disabled to mitigate risk during upgrades, incidents, or suspicious activity.
• Implemented related modifiers and checks on key functions to enforce paused state restrictions.

3. Codebase Updates and Refactoring

• Updated 8 files across the contract codebase to integrate the new security and administrative features.
• Refactored existing logic as needed to ensure compatibility with the new modifiers and state variables.
• Streamlined error messages, event emissions, and documentation comments where applicable.

4. Testing and Validation

• Added or updated tests to cover the new reentrancy guard and pause/unpause flows.
• Validated that only authorized roles can engage the pause/unpause features.
• Confirmed that all protected functions revert or behave as expected when the contract is paused or in a reentrancy attempt.

Impact

• Security: Greatly enhances contract security, reducing the attack surface for reentrancy exploits.
• Operational Flexibility: Empowers administrators to respond quickly to threats or incidents via the pause feature.
• Maintainability: Lays the groundwork for future security and administrative enhancements.

[Iwueseiter]

Nice work @Akshola00