Downloaded files are always stored as .bin instead of preserving the original extension

[Dkkathiriya]

Plugin: flutter_cache_manager
Version: ^3.4.1

When downloading media files (e.g., .mp4, .jpg, etc.) using CacheManager.downloadFile(), the cached file is always stored with a .bin extension, regardless of the original URL's file extension.

This creates confusion when trying to:

Use file types based on extension (e.g., previewing .mp4 in a video player)

Debug or manage cache files

Persist/restore with accurate file type outside the cache manager