Properly constrain `detail::copy` optimization (#4474) #8318

Job	Run time
mingw (mingw64)	3m 43s
mingw (ucrt64)	3m 55s
build (windows-2019, Win32, v142, 17, Debug)	1m 29s
build (windows-2019, Win32, v142, 17, Release)	2m 6s
build (windows-2019, x64, v141, 14, Release)	2m 7s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 8s
build (windows-2019, x64, v142, 20, Debug)	1m 36s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 28s
build (windows-2019, x64, v141, 17, Release)	2m 15s
build (windows-2019, x64, v141, 17, Debug)	1m 50s
build (windows-2022, x64, v143, Debug, 20)	1m 40s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 18s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 12s
build (windows-2019, x64, v142, 17, Debug)	1m 24s
build (windows-2019, x64, v142, 17, Release)	2m 14s
build (windows-2019, x64, v142, 20, Release)	2m 40s
build (windows-2019, x64, v141, 14, Debug)	1m 23s
	35m 28s

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