Function sswt_into 

pub fn sswt_into(
    signal: &Signal<f64>,
    config: &SSWTConfig,
    out: &mut SSWTResult,
) -> Result<()>

Forward SST writing into a caller-supplied result. Reuses every Vec in out (coefficients, frequencies, instantaneous_frequency, time), so rolling-window callers can amortize their cost across windows. Scalar metadata fields are overwritten unconditionally.