Function skopeo_bin 

pub fn skopeo_bin() -> &'static str

Return the skopeo binary path, honouring the BOOTC_EXP_EXTERNAL_CONTAINER_TOOL environment variable so callers can substitute an alternative tool (e.g. dtool) without hard-linking it as /usr/bin/skopeo. The _EXP prefix indicates this interface is experimental and subject to change.