Improved DIIS and gr Pulay mixing
Description
Refactoring of the mixing code. The matrix to be inverted in both GRPullay and DIIS are now computed with the same numerical stabilization as the Johnson approach, which can be viewed as a Tikhonov regularization in the case of the DIIS algorithm. This improvees the stability of the mixing in the testes cases.
News snippet
Improved stability for Pulay and DIIS mixings.
Checklist
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I have checked that my code follows the Octopus coding standards -
I have added tests for all the new features added in this request.