nut_player/nut_player_platform_interface

At first I run

flutter create --template=package hello

then add dependency plugin_platform_interface (https://pub.dev/packages/plugin_platform_interface) that prevent implement for platform-side classes

flutter pub add plugin_platform_interface

Extending a platform interface ensures that subclasses will get the default implementations from the base class, while platform implementations that implements their platform interface will be broken by newly added methods.