feat: add clean_newline utility for hyphenated line breaks (#2513)

[DevAbdullah90]

Problem

Issue #2513 identified a need for a utility function to handle hyphenated words split across newlines (e.g., "re- \nsearch" → "research"). This is a common issue in document partitioning where layout-preserving text extraction introduces artificial breaks in words.

Solution

This PR adds the clean_newline function to unstructured/cleaners/core.py.

• Logic: Uses regex r"(\w+)-\s+(\w+)" to rejoin hyphenated words.
• Flexibility: The \s+ pattern ensures it handles single spaces, tabs, and newlines between the hyphen and the word continuation.

Changes

• Added clean_newline to unstructured/cleaners/core.py.
• Added test cases to test_unstructured/cleaners/test_core.py covering various indentation and newline scenarios.

Verification

• Added parameterized unit tests in test_unstructured/cleaners/test_core.py.
• Verified all core cleaning tests pass (91 passed).

Fixes #2513

uv run python -m pytest test_unstructured/cleaners/test_core.py