docs: Added documentation to use SuryaOCR via plugin docling-surya

[harrykhh]

This PR integrates Surya as an optional layout analysis backend in Docling.

re: #2222

Key Changes

• Added SuryaLayoutModel in docling_core/layout_model.py to wrap Surya's detection API.
• Expanded tests and docs with Surya usage examples and benchmarks.

Non-breaking, modular enhancement for improved layout accuracy on complex PDFs.

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

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[dolfim-ibm]

Unfortunately Surya is licenses as GPL and cannot legally be included in this software package (without license changes).

The integration of the OCR engine could anyway be done as a stand-alone plugin. See https://docling-project.github.io/docling/concepts/plugins/.

@harrykhh if you are willing to make such a plugin-package we will be glad to list and promote it in the Docling docs.

[harrykhh]

Thanks for the review, @dolfim-ibm I reverted commits and updated the documents only to include the plugin https://pypi.org/project/docling-surya/

[cau-git]

@harrykhh Great to see the docling-surya plugin. The example you provide looks fine. I would suggest adding somewhere in the comments that it brings a GPL license. Apart from that it would be fine to merge.

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[harrykhh]

I would suggest adding somewhere in the comments that it brings a GPL license. Apart from that it would be fine to merge.

Done. Thanks @cau-git