Breaking test 04-silicon into two parts

Description

Fixing a bug for kdotp with a single electron, floating-point exceptions in the QMR linear solver for zero-norm states, and adding a test for covering these cases. The magneto-optic part of the test 04-silicon is now moved to the test 27-Ar to make is faster.

News snippet

Bugfix for kdotp run mode.

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.