Map speedup (#6745)
* Speed up dataset mapping
* Fix missing columns
* Remove cache files cleanup
* Update examples/text_to_image/train_text_to_image_sdxl.py
* make style
* Fix code style
* style
* Empty-Commit
---------
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: Quentin Lhoest <42851186+lhoestq@users.noreply.github.com>
Co-authored-by: Quentin Lhoest <lhoest.q@gmail.com>
