Implement speedup for sparse CLVs. #2338

Job	Run time
build (ubuntu-gcc-11-20.04)	9m 58s
build (ubuntu-gcc-11-20.04)	5m 59s
build (ubuntu-gcc-11-22.04)	9m 58s
build (ubuntu-gcc-11-22.04)	6m 0s
build (ubuntu-gcc-11)	9m 55s
build (ubuntu-gcc-11)	5m 58s
build (ubuntu-gcc-12-debugoptimized)	9m 55s
build (ubuntu-gcc-12-debugoptimized)	5m 55s
build (ubuntu-gcc-13-DEBUG_MACHINE)	9m 55s
build (ubuntu-gcc-13-DEBUG_MACHINE)	5m 54s
build (ubuntu-gcc-14-sanitize)	9m 56s
build (ubuntu-gcc-14-sanitize)	5m 56s
build (ubuntu-gcc-14)	9m 55s
build (ubuntu-gcc-14)	5m 55s
build (ubuntu-clang-17)	9m 54s
build (ubuntu-clang-17)	5m 55s
build (macos-xcode-15-intel)	9m 56s
build (macos-xcode-15-intel)	5m 58s
build (macos-xcode-16-arm)	9m 36s
build (macos-xcode-16-arm)	5m 36s
build (windows)	9m 55s
build (windows)	5m 55s
	2h 53m 54s

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