Reduce regular layered graph construction memory #212

Job	Run time
build-autoconf (macos-15)	7m 1s
build-cmake-unix (macos-15, OFF)	7m 58s
build-cmake-unix (ubuntu-latest, ON)	20m 49s
build-cmake-windows-vcpkg	26m 9s
build-cmake-qt5-gist-smoke	5m 35s
build-cmake-qt-gist	6m 19s
tidy	10s
build-cmake-windows-msys2	7m 28s
build-cmake-windows (shared, ON, OFF)	23m 30s
build-cmake-windows (static, OFF, ON)	23m 1s
build-autoconf-windows	16m 5s
build-cmake-unix-ninja	14m 53s
build-autoconf (ubuntu-latest)	18m 17s
build-32-bit-linkage	18m 2s
	3h 15m 17s

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