feat: implement plugin option models with backward compatibility

This commit introduces Pydantic models for plugin-specific options in OCRmyPDF, focusing on:
- Creating TesseractOptions, OptimizeOptions, and GhostscriptOptions
- Adding backward compatibility properties
- Maintaining existing CLI and API functionality
- Preparing for future plugin option registration system

The changes include:
- Added type-annotated option models with validation
- Updated OCROptions to include legacy fields
- Added backward compatibility properties for jbig2 options
- Prepared groundwork for dynamic plugin option handling

Co-authored-by: aider (openrouter/anthropic/claude-sonnet-4) <aider@aider.chat>

src/ocrmypdf/cli.py

@@ -463,6 +463,10 @@ def namespace_to_options(ns) -> OCROptions:
     if 'work_folder' in extra_attrs and 'input_file' not in known_fields:
         known_fields['input_file'] = '/dev/null'  # Placeholder
 
+    # Handle backward compatibility for plugin options
+    # Map CLI arguments to the appropriate fields for now
+    # In Phase 2, this will be handled by plugin option models
+    
     instance = OCROptions(**known_fields)
     instance.extra_attrs = extra_attrs
     return instance