Improve thread load balancing #232

Job	Run time
linux_gcc_valgrind	1m 10s
linux_gcc (ubuntu-latest, Debug)	4m 50s
linux_clang (ubuntu-latest, Debug)	3m 43s
linux_gcc_sanitizers	2m 27s
linux_gcc (ubuntu-latest, Release)	2m 28s
linux_clang (ubuntu-latest, Release)	1m 12s
macos_clang (macos-latest, Debug)	1m 40s
macos_clang (macos-latest, Release)	46s
windows_mingw64 (windows-latest, Debug)	5m 17s
windows_msvc2022	2m 33s
windows_mingw64 (windows-latest, Release)	2m 41s
	28m 47s

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