feature: parallel solve subspace diagonalization in dav_subspace #9746

Job	Run time
Build with GNU toolchain	4m 50s
Build with Intel toolchain	4m 8s
Build extra components with GNU toolchain	4m 49s
Build extra components with Intel toolchain	3m 51s
Build with CUDA support	4m 55s
Build without LCAO	4m 46s
Build without ELPA	4m 14s
Build without MPI	4m 15s
Build without LCAO and MPI	3m 45s
	39m 33s

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