build

nix: include `watchman` in dev shell #11979

Job	Run time
Build jj-lib without Git support	44s
cargo-deny (advisories)	24s
build (ubuntu-latest)	4m 6s
Check protos	30s
cargo-deny (bans licenses sources)	27s
build (macos-14)	3m 12s
Clippy check	2m 37s
build (windows-latest)	8m 35s
Check that MkDocs can build the docs with Poetry 1.8	30s
Check that MkDocs can build the docs	27s
build (ubuntu-latest, --all-features)	5m 0s
Check formatting	17s
	26m 49s

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