This makes a tidy data frame of stuff, and also changes things back to factors, if the levels are provided.
tidy_mcmc_coll_rep_stuff(field, p, pname, car_tib)
The output to tidy (i.e.. out$mean)
the name of the parameter whose values you want to extract (like "pi")
the name that you want the parameter to be called in the output
a tibble with repunit and collection in the order they appear in the output