fix(reading-order): dehyphenate hard continuations

[Success6666]

Summary

• remove a hard hyphen when a merged cross-element continuation begins with a lowercase character
• retain the existing soft-hyphen behavior and preserve hard hyphens before uppercase continuations
• add regression coverage using the production TextElement and ListItem types

Issue resolved by this Pull Request:

Resolves #3886.

Related issue

Refs #3881. The companion mapping change is in docling-project/docling-ibm-models#171.

Tests

• uv run pytest tests/test_readingorder_hyphenated_merges.py tests/test_readingorder_table_orientation.py -q
• uv run ruff check docling/models/stages/reading_order/readingorder_model.py tests/test_readingorder_hyphenated_merges.py
• uv run ruff format --check docling/models/stages/reading_order/readingorder_model.py tests/test_readingorder_hyphenated_merges.py
• uv run tach check

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]

lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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