Function resolve_hosts_expression 

pub async fn resolve_hosts_expression(
    backend: &StaticBackendDispatcher,
    shasta_token: &str,
    hosts_expression: &str,
    is_include_siblings: bool,
) -> Result<Vec<String>, Error>

Convenience wrapper that fetches node metadata from the backend and resolves a hosts expression to a sorted, deduplicated list of xnames.

This combines the two-step pattern of backend.get_node_metadata_available() followed by from_hosts_expression_to_xname_vec() that appears in many command files.