Implement Token Vesting Contract

### Description:

**Overview:**
Token vesting contracts allow tokens to be locked for a certain period, gradually releasing them to the beneficiary according to a predefined schedule. Implementing a token vesting contract for SimpleBitcoin will enable controlled distribution of tokens to team members, advisors, or investors, promoting long-term commitment and alignment of incentives.

**Proposed Changes:**

**Design Vesting Contract:** Define the structure and logic of the token vesting contract, including parameters such as vesting duration, cliff period, and release schedule.
**Integration with SimpleBitcoin:** Integrate the token vesting contract with the SimpleBitcoin token, allowing vested tokens to be transferred and managed within the same ecosystem.
**Deployment and Testing:** Deploy the token vesting contract to the Ethereum blockchain and conduct thorough testing to ensure its functionality and security.
**Documentation and Usage Guide:** Provide comprehensive documentation for users and beneficiaries on how to interact with the token vesting contract, including instructions for claiming vested tokens.

**Additional Considerations:**

Consider implementing customizable vesting schedules to accommodate different token distribution scenarios.
Explore options for extending vesting contracts with additional features such as revocability or token cliffs.
Labels:

- **feature**
- **tokenomics**
- **smart contract**