Refactoring of the SIC code:

Description

Refactoring of the SIC code:

• The ADSIC is now properly computed for the unpolarized case and now also computes the energy.
• The polarized and unpolarized cases are now giving exaclty the same result for close-shell systems.
• A test is added for this.

News snippet

Bugfix for ADSIC in the unpolarized case. ADSIC now properly computes the energy.

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.