build

Implement `transform_descendants()`, rewrite `jj parallelize` #10547

Job	Run time
Check protos	28s
build (ubuntu-latest)	4m 9s
cargo-deny (advisories)	27s
Clippy check	2m 23s
build (macos-14)	3m 1s
cargo-deny (bans licenses sources)	26s
build (windows-latest)	40s
Check that MkDocs can build the docs	25s
Check that MkDocs can build the docs with Poetry 1.3.2	47s
build (ubuntu-latest, --all-features)	5m 17s
Check formatting	17s
	18m 20s

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