Explicit KLI for noncollinear spins

Description

Reimplementing KLI for spinors, especially including the explicit solution of the equation. The solution is built using the solution of a Sylvester equation, which make both the Slater part and the KLI part more stable than the current implementation. This solves a bug of KLI for spinors erasing the xc potential (thus been wrong if correlation were included). A test is added to compare and test KLI for collinear and noncollinear spins.

News snippet

Reimplementing KLI for spinors, especially including the explicit solution of the equation.

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.