restore `(debug-level 2)` behavior, but reduce its guarantees (#834) #273

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	29m 10s
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	29m 10s
ci (a6osx, macos-12)	15m 14s
ci (a6osx, macos-12)	15m 14s
ci (ta6osx, macos-12)	18m 6s
ci (ta6osx, macos-12)	18m 6s
ci (arm64osx, macos-14)	13m 27s
ci (arm64osx, macos-14)	8m 27s
ci (tarm64osx, macos-14)	11m 9s
ci (tarm64osx, macos-14)	11m 9s
ci (i3le, ubuntu-22.04)	11m 12s
ci (i3le, ubuntu-22.04)	11m 12s
ci (ti3le, ubuntu-22.04)	14m 25s
ci (ti3le, ubuntu-22.04)	14m 25s
ci (a6le, ubuntu-22.04)	8m 52s
ci (a6le, ubuntu-22.04)	8m 52s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	11m 48s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	11m 48s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 20s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 20s
ci (i3nt, windows-2022, vs)	10m 45s
ci (i3nt, windows-2022, vs)	10m 45s
ci (ti3nt, windows-2022, vs)	14m 36s
ci (ti3nt, windows-2022, vs)	14m 36s
ci (a6nt, windows-2022, vs)	11m 45s
ci (a6nt, windows-2022, vs)	11m 45s
ci (ta6nt, windows-2022, vs)	14m 50s
ci (ta6nt, windows-2022, vs)	14m 50s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 46s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 46s
	6h 49m 50s

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