ENH Make PEFT configs forward compatible

[BenjaminBossan]

Right now, loading a PEFT config saved with a more recent PEFT version than is currently installed will lead to errors when new arguments are added to the config in the newer PEFT version. The current workaround is for users to manually edit the adapter_config.json to remove those entries.

With this PR, PEFT will make an attempt at removing these unknown keys by inspecting the signature. The user will be warned about these removed keys. This should generally be a safe measure because we will generally not introduce new config settings that change the default behavior. However, if a non-default is used, this could lead to wrong results. For this reason, users are urged in the warning to upgrade PEFT.

While working on the tests, I also converted the unittest.TestCase to a normal pytest test in order to be able to use pytest fixtures.

I also plan on adding the PEFT version to the adapter_config.json in the future. This will allow us to better handle compatibility issues in the future. As adding that new key to all PEFT configs could cause a lot of disruption, I want to get this PR in first to ensure forward compatibility.

Note that this new mechanism will not help anyone using a PEFT version <= 0.12.0, so this will be a slow transition.

[HuggingFaceDocBuilderDev]

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[BenjaminBossan]

Let's wait for #1996 to be merged first, than update this branch and make the two changes work together nicely.

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

[BenjaminBossan]

Not stale, still waiting for that PR, should be done soon.