[BC] Fix BC for other libraries

[ArthurZucker]

What does this PR do?

Fixes #29783

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[amyeroberts]

Thanks!

This works but I wonder if we want a more general fix for something like this in future or maybe design guidelines. If we have a model with many nested layers, we don't want a chain of many getattrs

[ArthurZucker]

For sure. accessing the past_key_values should maybe be done via a getter or rely on generation_config.cache_implementation!