feat: implement governance plugin with improved security and maintain…

[SimardeepSingh-zsh]

…ability

This commit introduces a comprehensive implementation of the governance plugin for the Solana program. The plugin enables users to deposit and withdraw governance tokens, with their voting weight being calculated based on the token types and amounts held.

Key features and improvements:

• Modular design with separate files for each functionality (error handling, account data structures, instructions, etc.), improving code organization and maintainability.
• Robust error handling with a dedicated RegistrarError enum, ensuring better error management and debugging.
• Secure token transfer operations using the spl_token crate, preventing potential vulnerabilities and adhering to best practices.
• Comprehensive test suite covering various scenarios, including different governance token types, invalid amounts, and insufficient balances, ensuring thorough testing and catching edge cases.
• Efficient account data structures using the borsh crate for serialization and deserialization, optimizing storage and performance.
• Integration with the spl-governance program, enabling seamless interaction with the governance system.
• Detailed documentation and comments throughout the codebase, facilitating easier onboarding and maintenance.

This implementation prioritizes security, reliability, and maintainability, providing a solid foundation for further development and integration with the broader Solana ecosystem.