build

Proof of concept: structured diff of conflicted commits #13220

Job	Run time
Check protos	30s
build (ubuntu-latest)	4m 30s
Build jj-lib without Git support	43s
build (macos-14)	3m 38s
build (windows-latest)	10m 28s
Check formatting	29s
build (ubuntu-latest, --all-features)	5m 29s
cargo-deny (advisories)	23s
Clippy check	2m 43s
Check that MkDocs can build the docs	20s
cargo-deny (bans licenses sources)	27s
Check that MkDocs can build the docs with Poetry 1.8	23s
	30m 3s

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