Introduce --ocr-engine option to select between OCR engines:
- 'auto' (default): Uses Tesseract
- 'tesseract': Explicit Tesseract selection
- 'none': Skip OCR entirely (for PDF processing only)
Key changes:
- Extend OcrEngine ABC with generate_ocr() and supports_generate_ocr()
for direct OcrElement tree output (bypasses hOCR)
- Add get_ocr_engine(options) hook parameter for engine selection
- Implement NullOcrEngine for --ocr-engine none
- Export OcrElement, OcrClass, BoundingBox from ocrmypdf package
- Add ocr_tree support to grafting pipeline
This prepares the foundation for pluggable OCR engines while maintaining
full backward compatibility with existing Tesseract-based workflows.
Replace inheritance from pluggy.PluginManager with composition pattern,
providing a type-safe interface for all 16 hooks defined in pluginspec.py.
The underlying pluggy manager is now accessible via the .pluggy property
for advanced use cases like set_blocked().
This change enables IDE autocomplete and type checking for all hook calls
while maintaining full backward compatibility with the plugin system.
Might take time for big files. Pdf.open() potentially is expensive as well, but QPDF doesn't give us progress feedback for that.
Closes Show progress during postprocessing #1313
James R. Barlow