Refactor metadata handling to use unified provider system

- Replaced direct usage of Civitai client with a fallback metadata provider across all recipe parsers.
- Updated metadata service to improve initialization and error handling.
- Enhanced download manager to utilize a downloader service for file operations.
- Improved recipe scanner to fetch model information through the new metadata provider.
- Updated utility functions to streamline image downloading and processing.
- Added comprehensive logging and error handling for better debugging and reliability.
- Introduced `get_default_metadata_provider()` for simplified access to the default provider.
- Ensured backward compatibility with existing APIs and workflows.

py/routes/update_routes.py

@@ -258,7 +258,7 @@ class UpdateRoutes:
         
         try:
             downloader = await Downloader.get_instance()
-            success, data = await downloader.make_request('GET', github_url, headers={'Accept': 'application/vnd.github+json'})
+            success, data = await downloader.make_request('GET', github_url, custom_headers={'Accept': 'application/vnd.github+json'})
             
             if not success:
                 logger.warning(f"Failed to fetch GitHub commit: {data}")
@@ -424,7 +424,7 @@ class UpdateRoutes:
         
         try:
             downloader = await Downloader.get_instance()
-            success, data = await downloader.make_request('GET', github_url, headers={'Accept': 'application/vnd.github+json'})
+            success, data = await downloader.make_request('GET', github_url, custom_headers={'Accept': 'application/vnd.github+json'})
             
             if not success:
                 logger.warning(f"Failed to fetch GitHub release: {data}")