feat(docx): add track changes (w:ins/w:del) support

[a-huk]

Add support for Word's Track Changes feature (also called Suggestions in
newer Word/Office 365 versions). Previously, inserted text (w:ins) and
deleted text (w:del) were silently dropped during DOCX conversion,
causing content loss.

New MsWordBackendOptions.track_changes field controls the behaviour:

• "accept" (default): include insertions, drop deletions — the final accepted document
• "reject": drop insertions, include deletions — the original document
• "raw": include both; insertions get underline formatting, deletions get strikethrough

Also exposed as --docx-track-changes CLI flag.

Issue resolved by this Pull Request:
Resolves #3152
Resolves #745

Checklist:

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

[github-actions]

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[mergify]

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[codecov]

Codecov Report

❌ Patch coverage is 10.86957% with 41 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/backend/msword_backend.py	4.65%	41 Missing ⚠️

📢 Thoughts on this report? Let us know!

[ceberam]

Thanks @a-huk for your interest in Docling and your contribution!

Before I dive in, should we nail down a few high-level details? I have the impression that we should first agree on the feature we want to support before code can be reviewed, since this is a completely new feature in Docling. By front-loading the design discussion we can save time and effort (you and the reviewers) and ensure that any code change are intentional, scoped, and aligned with the feature goals. Please, see the thread on the original issue and feel free to add your comments.

Thanks again for your work! 🎉

[PeterStaar-IBM]

@ceberam @a-huk Can we get this PR moving forward:

1. did we agree on the points in issue and how to tackle them?
2. Can we resolve the merge conflict and get this feature in Docling, it looks very promising!

[a-huk]

The change_type field needs to be added to TextItem in docling-core. I've temporarily patched the local venv's site-packages to add it (for testing), but this requires a separate docling-core PR.

[a-huk]

@PeterStaar-IBM let me know what you think of it now