feat: Add automatic OCR support for scanned PDFs

[anup00900]

• Add is_scanned_page() function to detect scanned vs native PDFs
• Add get_text_smart() method with automatic OCR detection
• Add to_markdown() methods for Page and Document classes
• Add document_to_markdown() for full document conversion

New API:

• page.is_scanned() - Detect if page is image-based
• page.get_text_smart() - Auto-apply OCR when needed
• page.to_markdown() - Convert page to Markdown with OCR
• doc.to_markdown() - Convert entire document to Markdown

These enhancements make PyMuPDF work seamlessly with scanned PDFs by automatically detecting and applying OCR when text extraction would otherwise return empty results.

This addresses a common user complaint about empty text extraction from scanned PDFs, though no specific issue was filed.

[github-actions]

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[anup00900]

I have read the CLA Document and I hereby sign the CLA

[JorjMcKie]

Thank you for your suggestion.

This feature is already included in package pymupdf4llm when being run in layout mode - see here.

It includes heuristics for deciding whether a page would indeed benefit from being OCR'd - far beyond the criteria present in this PR.

We will not duplicate efforts here. At a later point in time we might consider extending PyMuPDF's API by including calls to respective pymupdf4llm functions, but it is not among our pressing To Dos.

So I hoping for your understanding I am going to close this PR.