pub trait ListenerHandler {
// Required methods
fn get_addr(&self) -> &SocketAddr;
fn get_tags(&self, key: &str) -> Option<&CachedTags>;
fn set_tags(&mut self, key: String, tags: Option<BTreeMap<String, String>>);
// Provided method
fn get_concatenated_tags(&self, key: &str) -> Option<&str> { ... }
}