move away from foreach inside of int_pctl()

[topepo]

Use a pure future implementation with the new grouping method in rsample.

[topepo]

Current comments about rsample:

  #  TODO Changes in https://github.com/tidymodels/rsample/pull/465
  #  will effect how these computations are done since they will
  #  compute intervals for `terms` as well as any columns that begin
  #  with a period. This will simplify the code considerably for
  #  survival and non-survival models. We will make this version
  #  compatible with the future rsample version (but will factor
  #  this code later).

[github-actions]

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