[`PEFT`] Fix PEFT multi adapters support (#26407)
* fix PEFT multi adapters support
* refactor a bit
* save pretrained + BC + added tests
* Update src/transformers/integrations/peft.py
Co-authored-by: Benjamin Bossan <BenjaminBossan@users.noreply.github.com>
* add more tests
* add suggestion
* final changes
* adapt a bit
* fixup
* Update src/transformers/integrations/peft.py
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
* adapt from suggestions
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Co-authored-by: Benjamin Bossan <BenjaminBossan@users.noreply.github.com>
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
