Optimize `merge` algorithm for largest data sizes #10926

Job	Run time
codespell	14s
clang-format	1s
documentation	1s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
FPGA_EMU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=omp,cmplr=clang++,macos-latest,std=c++17,cfg=release	4m 9s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=icx-cl,windows-latest,std=c++17,cfg=release	4m 55s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=cl,windows-latest,std=c++17,cfg=release	6m 5s
HOST,bknd=omp,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	1s
CPU,bknd=dpcpp,cmplr=icx,windows-latest,std=c++17,cfg=release	5m 6s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=omp,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=serial,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	1s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	1s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	1s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	1s
	20m 46s

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