Fix Umklapp for HF singularity
Description
The Coulomb singularity was not handling properly the Umklapp for the q vector, leading to numerical instabilities and divergences for full range hybrids with k-points.
News snippet
Bugfix for Coulomb singularity for full range hybrids with k-points.
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.