unique name for each plugin instance

[mockersf]

Instead of marking the plugin as not unique, give it a unique name depending on the state it's loading in.

This means that

        // Add plugin for the splash screen
        .add_plugin(
            ProgressPlugin::new(AppState::Splash)
                .continue_to(AppState::MainMenu)
                .track_assets(),
        )
        // Add plugin for our game loading screen
        .add_plugin(ProgressPlugin::new(AppState::GameLoading).continue_to(AppState::InGame))

will work, but

        // Add plugin for the splash screen
        .add_plugin(
            ProgressPlugin::new(AppState::Splash)
                .continue_to(AppState::MainMenu)
                .track_assets(),
        )
        // Add plugin for our game loading screen
        .add_plugin(ProgressPlugin::new(AppState::Splash).continue_to(AppState::InGame))

won't, blocking adding by mistake the plugin twice with the same state

[inodentry]

Interesting. OK, i like this, helps improve correctness. Merging the PR, but im not sure this is worth making another release for... 🤔