Introduce Stateful Callbacks (#29666)
* Introduce saveable callbacks
* Add note
* Test for non-present and flag
* Support early stopping and refusing to train further
* Update docstring
* More saving
* Import oopsie
* Apply suggestions from code review
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
* Make it go through TrainerArguments
* Document
* Fix test
* Apply suggestions from code review
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
* Rework to allow for duplicates
* CLean
* Fix failing tests
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Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
