vine: count child_count properly in the transfer server process #563

Job	Run time
build-conda-linux	6m 37s
build-conda-macos-arm64 (macos-14)	6m 18s
build-conda-macos-x86_64 (macos-14)	5m 8s
build-native-linux (almalinux8)	6m 1s
build-conda-macos-x86_64 (macos-13)	9m 4s
build-native-linux (almalinux9)	7m 27s
lint	38s
build-native-linux (ubuntu20.04)	5m 49s
build-native-linux (ubuntu22.04)	5m 35s
build-native-linux (ubuntu24.04)	7m 12s
	59m 49s

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