docs: improve docstring scheduling folder - last batch

[delmalih]

What does this PR do?

This PR improves the docstrings and type hints in src/diffusers/schedulers/scheduling_ltx_euler_ancestral_rf.py, src/diffusers/schedulers/scheduling_utils.py and src/diffusers/schedulers/scheduling_vq_diffusion.py to follow the project conventions as described in #9567.
Fixes #9567

Context

This is part of a broader effort to improve documentation across all scheduler files in src/diffusers/schedulers/. See issue #9567 for details.

Testing

• Code passes make style
• Code passes make quality
• Code passes make fix-copies
• Existing tests still pass

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?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? issue.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests? (N/A - documentation only changes)

Who can review?

cc @stevhliu for review

[stevhliu]

Huge thanks for nearly single-handedly improving all these docstrings 👏 !

[stevhliu]

I wonder if removing all these args and replacing with a generic kwargs (even though it does avoid duplicating ConfigMixin.load_config), it'd make it more difficult for users to discover what they are? wdyt @sayakpaul ?

[delmalih]

Good point! I initially grouped them under kwargs to keep the documented arguments aligned with the explicit signature and avoid duplicating ConfigMixin.load_config. But I agree that keeping the forwarded loading options documented here is more helpful for discoverability. I’ll restore them while keeping the added type hints and Returns section.

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