onRestart property
Called when the user taps "Restart now" on the update banner, and forwarded to bannerBuilder.
The SDK cannot restart the app itself — Flutter has no process-restart
API — so wire this to whatever your app already uses (e.g.
Phoenix.rebirth(context) from the flutter_phoenix package, or a
root-widget rebuild). When null, the default banner hides the
restart button and only tells the user the patch applies next launch.
Implementation
final VoidCallback? onRestart;