>V</code> of the sandwich
  estimator of the covariance matrix of the parameters to be passed to
  <code><a href="https://paulnorthrop.github.io/chandwich/reference/adjust_loglik.html" class="external-link">adjust_loglik</a></code>.  In most cases, <code>cluster</code>
  must have length equal to the number of observations in data.  The
  exception is the GP (only) model (<code>binom = FALSE</code>), where the
  <code>cluster</code> may either contain a value for each observation in the raw
  data, or for e