build

Implement hacky variant of `jj purge` #13518

Job	Run time
Check protos	23s
build (ubuntu-latest)	4m 20s
cargo-deny (advisories)	20s
build (macos-14)	3m 35s
Build jj-lib without Git support	43s
cargo-deny (bans licenses sources)	22s
Clippy check	2m 40s
build (windows-latest)	9m 3s
build (ubuntu-latest, --all-features)	5m 21s
Check that MkDocs can build the docs	24s
Check that MkDocs can build the docs with Poetry 1.8	27s
Check formatting	18s
	27m 56s

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