Function open_postgres 

pub fn open_postgres<O, V>(
    connection_string: &str,
    oracle: Option<Arc<O>>,
    vector: Option<Arc<V>>,
    config: EngineConfig,
) -> Result<EngineHandle<PostgresPersistenceStore, O, V>, PostgresStoreError>
where
    O: OraclePort + Send + Sync + 'static,
    V: VectorPort + Send + Sync + 'static,

Convenience constructor: build a PostgresEngine<O, V> (an EngineHandle backed by PostgresPersistenceStore) from a connection string.

This is the recommended entry point for callers that want the full async EngineHandle.