build

Proof of concept: structured diff of conflicted commits #13629

Job	Run time
build (ubuntu-latest)	4m 34s
Build jj-lib without Git support	43s
build (macos-13)	7m 24s
build (macos-14)	4m 12s
cargo-deny (advisories)	24s
build (windows-latest)	8m 12s
cargo-deny (bans licenses sources)	24s
build (ubuntu-latest, --all-features)	5m 31s
Check protos	45s
Check that MkDocs can build the docs	23s
Check that MkDocs can build the docs with Poetry 1.8	25s
Check formatting	15s
Clippy check	2m 23s
	35m 35s

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