🔧 Add #[allow(dead_code)] to unused items

- Suppress dead code warnings for utility functions, enums and traits not yet used in production
- Reorganize imports to follow module conventions (e.g., `DeviceIdentity` moved earlier in openhome_renderer.rs)
- Improve formatting of ClientMessage variants for readability
These changes prepare codebase groundwork without altering runtime behavior.

pmoplaylist/src/persistence/mod.rs

@@ -333,6 +333,7 @@ impl PersistenceManager {
     }
 
     /// Supprime tous les tracks contenant un cache_pk donné
+    #[allow(dead_code)]
     pub async fn remove_by_cache_pk(&self, cache_pk: &str) -> Result<()> {
         let conn = self.conn.lock().unwrap();
         conn.execute("DELETE FROM tracks WHERE cache_pk = ?1", params![cache_pk])