Function rolling_sqrt_mean

crates/openquant/src/util/volatility.rs:161–166

(values: &[f64], window: usize)

/// `NaN` for the first `window - 1` bars; `window == 0` gives all `NaN`. Like Parkinson it
/// ignores overnight gaps. The name keeps mlfinlab's spelling (`get_garman_class_vol`).
///
/// # Errors
///
/// [`InputError`] if `high`, `low` or `close` differs in length from `open`.
///
/// ```
/// use openquant::util::volatility::get_garman_class_vol;
///
/// let vol = get_garman_class_vol(