Refactor RDMFT and ESolver classes for improved optimization structure

- Enhanced RDMFT class to support joint optimization on Stiefel manifold and occupation numbers on Euclidean space.
- Introduced RDMFT_Orbital and RDMFT_Occupation classes for separate optimization routes.
- Updated ESolver_DirectMin_LCAO to accommodate new optimization strategies, including hybrid two-level optimization.
- Added comprehensive setup functions for initializing problems and solvers.
- Improved energy and gradient computation methods for better performance.
- Cleaned up includes and organized class members for clarity and maintainability.

Author: Kai Luo