Function dispatch_input 

fn dispatch_input<'a>(
    session: &'a mut CqlSession,
    config: &'a MergedConfig,
    shell: &'a mut ShellState,
    input: &'a str,
) -> Pin<Box<dyn Future<Output = ()> + 'a>>

Dispatch a complete input line/statement to the session.

Handles built-in shell commands and CQL statements. Uses Box::pin to support recursive calls from execute_source.