#40 Implement folder-based model detection and caching mechanism

This implementation introduces a folder-based model detection approach and caching mechanism to improve model loading performance and reliability. ## Key Changes: ### 1. Enhanced ModelInfo Structure - Added caching-related fields: cacheValid, cacheModifiedAt, cachePathType, useFolderBasedDetection, detectionSource ### 2. ModelPathSelector Class - Determines path selection based on directory location - Models in "checkpoints" directory use model_path - Models in "diffusion_models" directory use diffusion_model_path - Includes fallback to architecture-based detection with logging ### 3. ModelDetectionCache Class - Thread-safe caching system for detection results - Cache validation based on file modification times - Reduces redundant model file parsing ### 4. Updated StableDiffusionWrapper - Uses folder-based path selection instead of architecture-based detection - Removes redundant model detection call in loadModel() - Preserves fallback mechanism for backward compatibility ### 5. Enhanced ModelManager - Integrates caching system during model scanning - Uses cached results when available - Implements cache invalidation when files are modified ## Benefits: - Faster model loading through folder-based detection - Reduced I/O operations through caching - Better reliability with directory-based path selection - Maintained backward compatibility - Improved debugging with detailed logging ## Files Modified: - include/model_manager.h - src/model_manager.cpp - src/stable_diffusion_wrapper.cpp