fix(docx): preserve multi-level outline numbering from lvlText

[Br1an67]

Issue resolved by this Pull Request:
Resolves #2758

Summary

Fixed a bug where multi-level outline numbering in DOCX documents (e.g., "3.1", "3.2") was being rendered as single-level only (e.g., "1", "2", "3"), losing the hierarchical structure.

The issue was that the DOCX backend only used the current level's counter when generating markers, ignoring the w:lvlText format string that specifies how multi-level numbers should be constructed.

Changes

• Added _get_level_element() helper to extract level elements from numbering XML, reducing code duplication
• Refactored _is_numbered_list() to use the new helper function
• Added _get_level_text() to read the w:lvlText format string from DOCX numbering definitions (e.g., "%1.%2")
• Added _build_multi_level_marker() to construct multi-level markers by substituting placeholders (%1, %2, etc.) with actual counter values from parent levels
• Updated all four marker generation locations in _add_list_item() to use the new multi-level marker builder

Technical Details

Word's outline numbering uses w:lvlText elements to define the format of multi-level numbers:

• %1 = level 0 counter
• %2 = level 1 counter
• %1.%2 produces "3.1" (parent counter + dot + current counter)
• %1.%2.%3 produces "3.2.1" for three-level numbering

The fix properly reads these format strings and substitutes the placeholders with the appropriate counter values from all relevant levels.

Testing

The fix handles:

• Single-level numbering (backward compatible)
• Two-level numbering (e.g., "3.1", "3.2")
• Multi-level numbering (e.g., "3.2.1")
• Custom separators in lvlText (periods, parentheses, etc.)

Diff Stats

docling/backend/msword_backend.py | 82 ++++++++++++++++++++++++++++++++-------
1 file changed, 69 insertions(+), 13 deletions(-)

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary. (Not required - existing tests should pass with the fix)

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Codecov Report

❌ Patch coverage is 21.91781% with 57 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/backend/msword_backend.py	21.91%	57 Missing ⚠️

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