Track the number of tokens seen to metrics (#27274)
* Add tokens seen
* Address comments, add to TrainingArgs
* Update log
* Apply suggestions from code review
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
* Use self.args
* Fix docstring
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
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Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
