[6008361][ONNX][Quantization] Clarify autotune guidance

[gcunhase]

What does this PR do?

Type of change: documentation

This PR clarifies when users should use ONNX quantization with Autotune enabled versus the direct Autotune entry point.

• Adds a warning to the Autotune guide explaining that direct Autotune is a lower-level Q/DQ placement tool and does not replace calibrated ONNX PTQ.
• Updates the ONNX quantization guide to show autotune=True in the Python API and explain that it uses default Autotune settings.
• Updates ONNX PTQ example documentation to prefer python -m modelopt.onnx.quantization ... --autotune=<mode> for accuracy-sensitive PTQ from an unquantized model.
• Updates the direct Autotune CLI help text to point users back to the full ONNX quantization workflow when calibration data and accuracy validation are required.

Usage

N/A — documentation/help text change.

Testing

• Ran python -m py_compile modelopt/onnx/quantization/autotune/__main__.py.
• Built the Sphinx documentation with python -m sphinx -b html docs/source docs/build/html; build succeeded. Remaining warnings are from optional documentation imports and existing cross-reference labels.

Before your PR is "Ready for review"

Make sure you read and follow Contributor guidelines and your commits are signed (git commit -s -S).

Make sure you read and follow the Security Best Practices (e.g. avoiding hardcoded trust_remote_code=True, torch.load(..., weights_only=False), pickle, etc.).

• Is this change backward compatible?: ✅
• If you copied code from any other sources or added a new PIP dependency, did you follow guidance in CONTRIBUTING.md: N/A
• Did you write any new necessary tests?: N/A
• Did you update Changelog?: N/A

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 2c4b081c-f24e-43db-8afa-58b7335c6fba

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.41%. Comparing base (c9dbb5e) to head (1ceaf68).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1989      +/-   ##
==========================================
- Coverage   77.40%   76.41%   -1.00%     
==========================================
  Files         524      524              
  Lines       59267    59649     +382     
==========================================
- Hits        45873    45578     -295     
- Misses      13394    14071     +677     

Flag	Coverage Δ
unit	54.79% <ø> (-0.20%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.