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/builtin_plugins/ghostscript.py

@@ -5,8 +5,10 @@
 from __future__ import annotations
 
 import logging
+from typing import Annotated
 
 from packaging.version import Version
+from pydantic import BaseModel, Field
 
 from ocrmypdf import hookimpl
 from ocrmypdf._exec import ghostscript
@@ -20,6 +22,13 @@ log = logging.getLogger(__name__)
 BLACKLISTED_GS_VERSIONS: frozenset[Version] = frozenset()
 
 
+class GhostscriptOptions(BaseModel):
+    """Options specific to Ghostscript operations."""
+    
+    color_conversion_strategy: Annotated[str, Field(description="Ghostscript color conversion strategy")] = "LeaveColorUnchanged"
+    pdfa_image_compression: Annotated[str, Field(description="PDF/A image compression method")] = "auto"
+
+
 @hookimpl
 def add_options(parser):
     gs = parser.add_argument_group("Ghostscript", "Advanced control of Ghostscript")