`check_model` and `plot.see_check_*` functions

Maybe it's just me, but the method for check_model seems really hard to expand / add to currently.

Would it not be easier to have check_model be a simple wrapper around the various plot.see_check_* functions, like this:

check_model <- function(model, ...) {
  plot(check_normality(model)) + 
    plot(check_homogeneity(model)) + 
    plot(check_collinearity(model)) + 
    plot(check_outliers(model)) + 
    patchwork::plot_layout(ncol = 2)
}

With the plotting methods for each check_* living peacefully in see?

(If it is just me, then I need someone to implement check_model.htest 😒)

Start by reading the existing check_model implementation and the plot.see_check_* functions, especially check_normality(), check_homogeneity(), check_collinearity(), and check_outliers(). Compare their current interfaces and determine whether check_model can delegate to them, including the requested htest behavior. Done means the expansion path and plotting composition are resolved and covered by appropriate checks.