- Implemented the `exists` method in `SandboxFileSource` and its subclasses to verify the availability of sandbox sources.
- Updated `SandboxFileService` to utilize the new `exists` method for improved error handling when listing files and downloading files.
- Removed the previous check for storage existence in `archive_source.py` and replaced it with the new method.
- Replaced direct storage references with SilentStorage in various components to enhance fallback mechanisms.
- Updated storage key formats for sandbox archives and files to improve clarity and consistency.
- Refactored related classes and methods to utilize the new SandboxFilePath structure.
- Adjusted unit tests to reflect changes in the StorageTicket model and its serialization methods.
- Removed unused app asset download and upload endpoints, along with sandbox archive and file download endpoints.
- Updated imports in the file controller to reflect the removal of these endpoints.
- Simplified the generator.py file by consolidating the code context field definition.
- Enhanced the storage layer with a unified presign wrapper for better handling of presigned URLs.
