compose: Stabilize `compose rootfs` #3211

Job	Run time
Build	16m 12s
Build (c9s)	20m 28s
cargo-deny	22s
Build Integration Test Data	1m 13s
Verify CXX generation	1m 43s
Differential ShellCheck	13s
compose-image tests	13m 32s
Container build	2m 14s
Compose tests	29m 33s
compose-rootfs tests	6m 43s
Encapsulate tests	2m 26s
Container Integration	4m 59s
experimental build-chunked-oci tests	3m 24s
	1h 43m 2s

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