Function settle 

pub async fn settle<F, Fut>(
    cfg: &SettleConfig,
    probe: F,
) -> Result<SettleOutcome, Error>
where
    F: FnMut() -> Fut,
    Fut: Future<Output = Result<Probe, Error>>,

Drive a settle loop: repeatedly call probe, folding each reading via [step] and sleeping poll_interval between calls, until the page settles or the timeout elapses. dt for each fold is the real elapsed time since the previous probe, so the loop is self-pacing.