Optimize LCAO for large systems and domain parallelization

Description

The LCAO now computes the overlap and Hamiltonian matrices only for atoms whose submeshes are touching. This allows for reducing the numerical burden for large systems.

News snippet

Optimization of LCAO for large systems using domain parallelization.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.