clean up "merge with root" handling and related revset evaluation #10088

Job	Run time
Check protos	33s
cargo-deny (advisories)	32s
Clippy check	2m 24s
build (ubuntu-latest)	3m 24s
cargo-deny (bans licenses sources)	30s
build (macos-14)	2m 54s
Check that MkDocs can build the docs	22s
build (windows-latest)	7m 33s
Check that MkDocs can build the docs with Poetry 1.3.2	41s
Check formatting	12s
build (ubuntu-latest, --all-features)	4m 13s
	23m 18s

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