Add missing Args: entries to scheduler docstrings

[4ktLuffy]

What does this PR do?

Adds the missing Args: entries reported in #14352 — sixteen scheduler methods had docstrings that omitted parameters present in their signature.

• noise — the DPMSolver singlestep/multistep and cosine-multistep update methods. Not optional in practice: the sde-* algorithm types do assert noise is not None, so a caller reading only the docstring has no way to learn the parameter exists.
• mu — DPMSolverMultistepScheduler.set_timesteps and DPMSolverSinglestepScheduler.set_timesteps. The entry also records the precondition (use_dynamic_shifting + time_shift_type="exponential"), since passing mu without them trips an assert.
• device — CogVideoXDDIMScheduler.set_timesteps and DDIMInverseScheduler.set_timesteps. Wording matches the existing device entries elsewhere in the schedulers.
• sigma / sigma_next / sigma_before — the Helios UniPC methods.

Also corrects rescale_zero_terminal_snr in scheduling_dpm_cogvideox.py, whose Args: block documented a betas parameter the function does not take — the signature is rescale_zero_terminal_snr(alphas_cumprod).

scheduling_dpmsolver_multistep_inverse.py was not hand-edited: that method is a # Copied from of scheduling_dpmsolver_multistep, so the change was propagated with make fix-copies per .ai/AGENTS.md.

Documentation only — no behavior change.

Fixes #14352

Coordination

#14352 is filed but has not yet been acknowledged by a maintainer, and the contributing guide asks for that acknowledgment first. I'm opening this rather than sitting on finished work, but I'd rather flag that than have it look like the step was skipped — happy to close this and wait if you'd prefer the order kept strictly.

Test commands and output

$ make quality
ruff check examples scripts src tests utils benchmarks setup.py
All checks passed!
ruff format --check examples scripts src tests utils benchmarks setup.py
2000 files already formatted
doc-builder style src/diffusers docs/source --max_len 119 --check_only
python utils/check_doc_toc.py

$ python -m pytest tests/schedulers/test_scheduler_dpm_multi.py \
    tests/schedulers/test_scheduler_dpm_single.py \
    tests/schedulers/test_scheduler_dpm_multi_inverse.py \
    tests/schedulers/test_scheduler_ddim_inverse.py -q

151 passed, 3 skipped, 24805 warnings in 59.18s

The AST scan that produced the issue's list — comparing each public method's signature against the parameter names in its Args: block — returns zero findings across src/diffusers/schedulers/ after this change.

Self-review notes

Run against .ai/review-rules.md.

Blocking issues: none.

Non-blocking — deliberately left for review:

1. rescale_zero_terminal_snr's docstring is wrong beyond the Args: block (scheduling_dpm_cogvideox.py). The summary says "Rescales betas…" and Returns: says "rescaled betas…", but the function takes alphas_cumprod and returns alphas_bar. I fixed only the Args: entry, since Scheduler docstrings omit real parameters (noise, mu, device, sigma*) across 16 functions #14352 is scoped to signature/docstring mismatches and widening the diff past the coordinated scope seemed worse than flagging it. Say the word and I'll fix the summary and Returns: here.

2. Doc-impact suggestion: "Args: entries must match the signature" isn't currently in .ai/review-rules.md, and the scan used here is small enough to run as a CI check. Raising it as a proposal only — CONTRIBUTING.md says .ai/ is maintainer-owned, so nothing under it is touched in this PR.

Dead code analysis: N/A — no new model, no code paths changed.

Accuracy: every description was traced to its use in the source rather than inferred from the parameter name — noise to the sde-dpmsolver++ assert, mu to flow_shift = np.exp(mu) and its preceding assert, and the Helios sigmas to sigma_t, sigma_s0 = sigma_next, sigma with the self.sigmas[step_index] fallback.

Verdict: READY — 8 files, +46/−2, documentation only.

Before submitting

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  • Did you read the Coding with AI agents guide?
  • Did you run the self-review skill on the diff?
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• Did you read our philosophy doc? (important for complex PRs)
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case. — discussed in Scheduler docstrings omit real parameters (noise, mu, device, sigma*) across 16 functions #14352 (not yet acknowledged, see Coordination above)
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests? — none needed; documentation only
• Are you the author (or part of the team) of the model/pipeline (only applicable for model/pipeline related PRs)?

[4ktLuffy]

Tagging for review — @stevhliu (docs; git blame shows most of the DPMSolver docstring bodies here are yours) and @dg845 (schedulers; the scheduling_helios.py docstrings are yours).

Documentation only, +46/-2, no behavior change. Self-review notes are in the PR description.

[HuggingFaceDocBuilderDev]

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[stevhliu]

thanks!