cli: consider "JJ:" lines as comments also when not followed by space #16866

Job	Run time
Build jj-lib without Git support	46s
Check protos	30s
cargo-deny (advisories)	22s
build (ubuntu-latest)	2m 55s
cargo-deny (bans licenses sources)	22s
Clippy check	2m 37s
build (macos-13)	2m 56s
Check that MkDocs can build the docs	8s
build (macos-14)	2m 57s
Check that MkDocs can build the docs with latest Python and uv	11s
build (windows-latest)	2m 42s
Check formatting	16s
build (ubuntu-latest, --all-features)	3m 2s
	19m 44s

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