Refactor/generalize new inference system

[lchoquel]

Added

• Unified OCR system using model handles instead of separate OcrHandle enum
• ModelType enum supporting LLM and TEXT_EXTRACTOR types
• Enhanced error handling in library loading with better validation messages
• Config template management with config-template and cft Makefile targets

Changed

• OCR system now uses InferenceModelSpec with unified model handles
• Renamed get_llm_deck() to get_model_deck() and updated parameter names from llm_handle to model_handle
• Simplified OCR worker factory using plugin SDK matching
• Enhanced plugin system compatibility with InferenceModelSpec
• Improved error messages throughout system

Removed

• Legacy OCR classes: OcrHandle, OcrPlatform, OcrEngine, OcrEngineFactory
• Obsolete configuration fields and setup methods
• PipelexFileError exception class

[thomashebrard]

ok