Code Migration & Optimization: CI 3 to 4, PHP 7 to 8

I need my application migrated from CodeIgniter 3 to 4 and from PHP 7 to PHP 8. The application features user authentication, data reporting, project management, invoicing, and estimating. While the migration is the main focus, the code also needs to be optimized to resolve current performance issues, namely slow loading times and high memory usage.

Ideal skills and experience:
- Proficiency in CodeIgniter and PHP
- Experience with code optimization
- Familiarity with performance troubleshooting
- Understanding of user authentication and data reporting systems
- Knowledge of project management, invoicing, and estimating software