Optimize `merge` algorithm for largest data sizes #10970

Job	Run time
clang-format	10s
codespell	12s
documentation	19s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	15m 17s
HOST,bknd=tbb,cmplr=icx-cl,windows-latest,std=c++17,cfg=release	17m 46s
FPGA_EMU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	25m 6s
HOST,bknd=omp,cmplr=clang++,macos-latest,std=c++17,cfg=release	4m 58s
HOST,bknd=tbb,cmplr=cl,windows-latest,std=c++17,cfg=release	15m 38s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	12m 11s
CPU,bknd=dpcpp,cmplr=icx,windows-latest,std=c++17,cfg=release	11m 9s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	10m 25s
HOST,bknd=omp,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	5m 59s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	8m 49s
HOST,bknd=tbb,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	9m 4s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	11m 3s
HOST,bknd=omp,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	8m 20s
HOST,bknd=tbb,cmplr=clang++,ubuntu-latest,std=с++17,cfg=release	11m 13s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++17,cfg=release	11m 59s
HOST,bknd=serial,cmplr=g++,ubuntu-latest,std=с++17,cfg=release	4m 59s
CPU,bknd=dpcpp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	27m 19s
HOST,bknd=tbb,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	17m 42s
HOST,bknd=omp,cmplr=icpx,ubuntu-latest,std=с++20,cfg=release	17m 43s
	4h 7m 21s

Provide feedback