SFutureButton class

A customizable button widget that handles asynchronous operations with automatic loading states.

The onTap callback returns a Future<bool?> to control the button's behavior:

• Returns true or completes successfully: Shows success animation
• Returns false: Shows error state with 'Validation failed' message
• Returns null: Resets button without showing success animation (silent dismissal)
• Throws exception: Shows error state with the exception message

Example usage:

SFutureButton(
  onTap: () async {
    // Perform validation
    if (someCondition) return null; // Dismiss without success
    if (!isValid) return false; // Show error

    // Perform the actual operation
    await someAsyncOperation();
    return true; // Show success animation
  },
  onPostSuccess: () {
    // Called only when onTap returns true
    print('Operation completed successfully');
  },
)