fix(example_images_download_manager): re-raise specific exception on download error
refactor(usage_stats): define constants locally to avoid conditional imports
test(example_images_download_manager): update exception handling in download tests
test(example_images_file_manager): differentiate between os.startfile and subprocess.Popen in tests
test(example_images_paths): ensure valid example images root with single-library mode
test(usage_stats): use string literals for metadata payload to avoid conditional imports
- Introduced a new `Downloader` class to centralize HTTP/HTTPS download management.
- Replaced direct `aiohttp` session handling with the unified downloader in `MetadataArchiveManager`, `DownloadManager`, and `ExampleImagesProcessor`.
- Added support for resumable downloads, progress tracking, and error handling in the new downloader.
- Updated methods to utilize the downloader's capabilities for downloading files and images, improving code maintainability and readability.
