Add `par_reduce_inner` functions #5357

Job	Run time
CI-Rocm-HIP (hipcc, Release, hip, serial)	33m 50s
CI-Cuda-Host (g++, Release, cuda, serial)	42m 22s
CI-Rocm-HIP (hipcc, Release, hip, mpi)	35m 4s
CI-Rocm-HIP (hipcc, Debug, hip, serial)	57m 54s
CI-Cuda-Host (g++, Release, cuda, mpi)	45m 0s
CI-Cuda-Host (g++, Release, host, serial)	12m 9s
CI-Rocm-HIP (hipcc, Debug, hip, mpi)	57m 22s
CI-Cuda-Host (g++, Release, host, mpi)	12m 43s
CI-Cuda-Host (g++, Debug, cuda, serial)	1h 15m 37s
CI-Cuda-Host (g++, Debug, cuda, mpi)	1h 18m 3s
CI-Cuda-Host (g++, Debug, host, serial)	11m 31s
CI-Cuda-Host (g++, Debug, host, mpi)	11m 16s
CI-Cuda-Host (clang++-15, Release, cuda, serial)	27m 40s
CI-Cuda-Host (clang++-15, Release, cuda, mpi)	28m 14s
CI-Cuda-Host (clang++-15, Release, host, serial)	11m 2s
CI-Cuda-Host (clang++-15, Release, host, mpi)	10m 32s
CI-Cuda-Host (clang++-15, Debug, host, serial)	8m 2s
CI-Cuda-Host (clang++-15, Debug, host, mpi)	8m 0s
	9h 26m 21s

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