Function ec2_list 

pub fn ec2_list(wrapper: &str, items: &[String]) -> String

Render a flattened EC2 list. wrapper is the set element name (e.g. instancesSet); each entry in items is the already-rendered inner XML of one <item> (do NOT pre-wrap entries in <item>).

An empty list still emits the wrapper element (<wrapper/>-equivalent), matching how the AWS SDKs expect an empty set to deserialize to [].