improve support for lists in cptypes #310

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	30m 4s
ci (a6osx, macos-12)	14m 9s
ci (ta6osx, macos-12)	20m 13s
ci (arm64osx, macos-14)	8m 42s
ci (tarm64osx, macos-14)	10m 43s
ci (i3le, ubuntu-22.04)	11m 19s
ci (ti3le, ubuntu-22.04)	14m 17s
ci (a6le, ubuntu-22.04)	8m 50s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	11m 50s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 8s
ci (i3nt, windows-2022, vs)	11m 45s
ci (ti3nt, windows-2022, vs)	14m 50s
ci (a6nt, windows-2022, vs)	12m 4s
ci (ta6nt, windows-2022, vs)	14m 47s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 42s
	3h 25m 23s

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