Refuse a split index that is not a row number, and an empty assessment set

[jmgirard]

The entry check of the nested drivers and nested_resamples() now refuse three more shapes of split row index, with class nestedtune_bad_design:

• an in_id or out_id that is not a numeric vector (character, factor, list, logical),
• a value outside integer range, such as 3e9 or Inf,
• an out_id that is NULL or empty.

The rule extends the existing NA refusal and runs before the shared-rows and containment rules. One error names every bad split and slot, each by its first shape. The logical NA out_id, rsample's mark for the complement, stays accepted.

Before, these designs passed the check and the fold failed inside rsample or vctrs, or an empty inner assessment set was left out of tuning with no message.

Local: devtools::test() 0 failures, devtools::check() 0 errors, 0 warnings, 0 notes.