Optimize `merge` algorithm for largest data sizes #200

Job	Run time
clang-format	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=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	1s
HOST,bknd=tbb,cmplr=icx-cl,windows-latest,std=c++17,cfg=release	8m 48s
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	10m 38s
HOST,bknd=omp,cmplr=clang++,macos-latest,std=c++17,cfg=release	5m 25s
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	9m 33s
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
	34m 40s

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