PreTrainedTokenizerFast
* draft solution * use `setdefault` * nits * add tests and fix truncation issue * fix test * test passes locally * quality * updates * update tsets
train_new_from_iterator
* Per-folder tests reorganization Co-authored-by: sgugger <sylvain.gugger@gmail.com> Co-authored-by: Stas Bekman <stas@stason.org>