Fix stale experimental.kto docstring cross-references in KTOTrainer/KTOConfig

[DaoyuanLi2816]

What does this PR do?

PR #6175 promoted KTO from trl.experimental.kto to the stable trl.trainer API — it moved kto_trainer.py/kto_config.py and updated the >>> from trl.experimental.kto import ... code examples, but left four docstring cross-references still pointing at the old experimental path.

In KTOTrainer.__init__'s docstring:

args ([`experimental.kto.KTOConfig`], *optional*):
...
Will default to [`~experimental.kto.kto_trainer.DataCollatorForUnpairedPreference`] if the model is a
language model and [`~experimental.kto.kto_trainer.DataCollatorForVisionUnpairedPreference`] if the model

And in KTOConfig's class docstring:

Configuration class for the [`experimental.kto.KTOTrainer`].

trl/experimental/kto/ now contains only a deprecation shim __init__.py (the kto_trainer submodule itself was deleted), so:

• the two collator references point at a module path that no longer exists (experimental.kto.kto_trainer isn't importable), and
• the KTOConfig/KTOTrainer references resolve only to shim subclasses whose __post_init__/__init__ raise FutureWarning: ... Update your imports to from trl import KTOConfig``.

So the stable class's own docstring points readers at the exact import path its own code warns against.

This PR updates all four references to the stable self-referential form, matching DPOTrainer's already-correct pattern:

args ([`DPOConfig`], *optional*):
...
Will default to [`~trainer.dpo_trainer.DataCollatorForPreference`] if the model is a language model and

and

Configuration class for the [`DPOTrainer`].

Docstring-only change, no behavior change.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline, Pull Request section?

---

Note

Low Risk
Documentation-only edits with no code or behavior changes.

Overview
After KTO moved to the stable trl.trainer API, four docstring links still pointed at experimental.kto paths that no longer exist or only resolve through deprecation shims.

This PR retargets them to match DPOTrainer / DPOConfig: KTOConfig now references [KTOTrainer]; KTOTrainer.__init__ references [KTOConfig] and the default collators under [~trainer.kto_trainer.*]. Docstrings only — no runtime or API behavior change.

^{Reviewed by Cursor Bugbot for commit 29942a4. Bugbot is set up for automated code reviews on this repo. Configure here.}

[DaoyuanLi2816]

Superseded by #6345 (merged just now), which fixes this same stale experimental.kto reference along with a broader KTO-stable-trainer docs pass. Closing.