rewrite using purrr

[almartin82]

the status percentile https://github.com/almartin82/mapvizieR/blob/c2f8f41892ff118fc1d066d140dc3d238d908316/R/mapvizier_summary.R#L160

[almartin82]

ie

      this_target$start_cohort_status_npr <-
        purrr::map(
          .x = this_target$baseline_rit, 
          .f = cohort_mean_rit_to_npr, 
          measurementscale = i, 
          current_grade = k, 
          season = 'Spring'
        )