fix: restore pptx mixed-script no-wrap titles

[developer0hye]

What changed

• restore no-wrap behavior for mixed-script PPTX titles after the text-extraction follow-up
• keep no-wrap state across styled run boundaries so CJK section titles and mixed-font headers stay on one line
• add regression coverage for mixed-script no-wrap titles and cross-run heading cases

Why

• main regressed on the KTB PPTX deck: slide 9 TOC and slides 20/30 headers wrapped again after fix: preserve no-wrap text extraction

Validation

• cargo test --offline -p office2pdf fixed_page_textbox_tests
• cargo test --offline -p office2pdf --test pptx_fixtures text_content_test_slides -- --nocapture
• rebuilt the CLI and visually rechecked slides 9, 20, and 30 in the regenerated PDF