build

config: replace LayeredConfigs with StackedConfig #16698

Job	Run time
build (ubuntu-latest)	5m 8s
Build jj-lib without Git support	45s
build (macos-13)	6m 47s
build (macos-14)	4m 24s
Check protos	27s
build (windows-latest)	10m 33s
Check formatting	20s
build (ubuntu-latest, --all-features)	6m 6s
Clippy check	2m 26s
cargo-deny (advisories)	26s
Check that MkDocs can build the docs with latest Python and uv	13s
cargo-deny (bans licenses sources)	23s
Check that MkDocs can build the docs	11s
	38m 9s

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