Add app's icon to files with a specific extension on Windows and Mac platforms

We have a Flutter-based desktop app that works on Windows, macOS, and Linux. We would like to add product icons to all files that have the .hypn extension specifically for Windows and macOS users. When our app encrypts a file, the encrypted file has a .hypn extension. This can be done as a script during the install process or done in Flutter.

All the app icons will be provided.