Function fill_smart 

pub async fn fill_smart(
    client: &CdpClient,
    session_id: &str,
    ref_map: &RefMap,
    selector_or_ref: &str,
    value: &str,
    iframe_sessions: &HashMap<String, String>,
) -> Result<(), String>

Smart fill matching DevTools agent fill semantics:

• <select> → option match by value or label
• checkbox/radio → "true"/"false" (radio true clicks to select)
• otherwise → text fill via insertText