Fix RAM usage by splitting deeply nested expressions #3027

Job	Run time
build_system	25s
duplicates	5s
spell_check	12s
build (gcc-15.deb, --std-tests)	6m 25s
build (gcc-15.deb, --test-libcore)	18m 2s
build (gcc-15.deb, --extended-regex-tests)	14m 18s
build (gcc-15.deb, --extended-regex-example-tests)	8m 20s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	15m 35s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	14m 37s
build (gcc-15.deb, --extended-rand-tests)	9m 24s
build (gcc-15.deb, --projects)	12m 32s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	13m 53s
build (gcc-15-without-int128.deb, --projects)	11m 4s
build (gcc-15-without-int128.deb, --extended-regex-tests)	12m 59s
build (gcc-15-without-int128.deb, --extended-regex-example-tests)	6m 46s
build (gcc-15-without-int128.deb, --test-libcore)	17m 52s
build (gcc-15-without-int128.deb, --std-tests)	7m 31s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	16m 32s
build (gcc-15-without-int128.deb, --extended-rand-tests)	10m 47s
success	2s
	3h 17m 21s

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