[Feature]: flutter_timer_countdown: Custom onEndWidget

[arnab]

Plugin name flutter_timer_countdown

Is your feature request related to a problem? Please describe. No, it's a new feature idea/request.

Request details / Describe the solution you'd like Currently, when the timer reaches zero, it displays "00:00" (or equivalent based on format). Many apps need to show a different message when a countdown expires.

It would be nice to have a onEndWidget or onDone optional Widget? parameter that replaces the timer when it expires.

Describe alternatives you've considered

This can be done right now by adding a piece of state to the widget that uses TimerCountdown. However, for simple widgets that can stay Stateless it can be made much easier if the TimerCountdown just took an additional parameter.