Make it clearer why this is being done. Something like, "The stat_fun used by the clustering functions takes data of shape XXX, and must return data of shape YYY. Our generalized two-way ANOVA function operates on data of shape ZZZ and returns F-values in the first output argument based on the requested condition. We must thus make a dummy function `stat_fun` to wrap to `r_anova_twoway()` that just returns F-values for the interaction term (our contrast of interest)."