add vesting contract

[JoE11-y]

📝 Add Vesting Contract

🛠️ Issue

• Closes [FEAT]: Implement vesting contract #110

📖 Description

PR Description: Vesting Contract Implementation

This PR introduces a robust Vesting Contract for managing token distribution schedules in a decentralized and automated manner. The contract is designed to handle the creation, management, and claiming of vesting schedules, ensuring fairness and flexibility for token allocations.

Key Features

1. Vesting Schedule Management:

   • Add schedules with specified start time, cliff time, end time, and total token allocation.
   • Support for partial vesting using percentages.

2. User Claims:

   • Users can claim tokens based on the amount vested at the current time.
   • Automatically calculates the vested and claimable amount based on elapsed time and schedule parameters.

3. Ownership Controls:

   • The contract is Ownable, ensuring only the owner can add or remove vesting schedules.
   • Allows the owner to end vesting schedules prematurely and manage refunds.

4. Error Handling:

   • Validations for edge cases, including:
     • Zero address or amount.
     • Invalid time configurations (e.g., end time before cliff time).
     • Percentage or token transfer errors.

5. Event Emissions:

   • Emits structured events for key actions, such as adding schedules, successful claims, and vesting terminations.

6. Integration:

   • Compatible with OpenZeppelin ERC-20 tokens using dispatcher interfaces for token transfers.
   • Designed for seamless integration with dApps and token distribution platforms.

🖼️ Screenshots (if applicable)

• Include any relevant screenshots or examples of the changes made. This helps reviewers visualize the updates

📝 Additional Notes

• Any additional context, questions, or considerations for the reviewers: