Fix OpenMP

Description

Fix some OpenMP clauses:

• For submeshes, the OpenMP calls are deactivated for overlapping sphere, as otherwise we need a reduction.
• Add missing private and firstprivate clauses in some calls
• Do not call BLAS within an OpenMP region
• Fix a wrong critical clause in the LCAO and replace it a proper accumulation

News snippet

Fix some OpenMP clauses.

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.