Fix summary export for ordered item parameters

[saudiwin]

See below for an ordered model of model_id = 4:

c1  <- summary(can_ideal, pars="items")
Error:
! Can't find the following variable(s) in the output: steps_votes
Hide Traceback
     ▆
  1. ├─base::summary(can_ideal, pars = "items")
  2. ├─idealstan::summary(can_ideal, pars = "items")
  3. │ └─idealstan (local) .local(object, ...)
  4. │   ├─... %>% bind_rows() at [idealstan/R/Generics.R:717:17](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)
  5. │   └─base::lapply(...)
  6. │     └─idealstan (local) FUN(X[[i]], ...)
  7. │       ├─... %>% as_draws_df at [idealstan/R/Helpers.R:1838:3](vscode-file://vscode-app/Applications/Positron.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html#)
  8. │       ├─posterior::as_draws_array(object@stan_samples$draws("steps_votes"))
  9. │       └─object@stan_samples$draws("steps_votes")
 10. ├─dplyr::bind_rows(.)
 11. │ └─rlang::list2(...)
 12. └─posterior::as_draws_df(.)