Title: Implementing a Toast Visibility Indicator in Fluttertoast

[mayank29malhotra]

This pull request addresses issue #496 by introducing a new feature in Fluttertoast that enables developers to use a variable to check if a toast is currently visible. The feature includes the addition of a boolean variable isToastVisible which indicates the visibility status of the toast.

This enhancement improves the user experience by preventing an excessive number of toasts from appearing successively and ensures that only relevant information is displayed to the user. The implementation follows best practices and maintains backward compatibility with existing code.

Testing Example I already added in the [ErrorSolvedTesting.dart] file and added a screenshot of the console here below:

Printing true while displaying

Printing false everytime else

Here value is printing every second to test the funtionality.

[spyingcoder]

@ponnamkarthik Please review and merge this. Must needed.