Fix single letter stop strings (#31448)
* Fix single letter stop strings
* Change the 0 to a 1 to avoid potential empty vector headaches later
* Restructure for clarity
* Update tests/generation/test_stopping_criteria.py
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
* Add the unsqueeze
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Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
