Improve example app callbacks

example/lib/home/widgets/scan_filter_widget.dart

@@ -3,7 +3,7 @@ import 'package:universal_ble/universal_ble.dart';
 import 'package:universal_ble_example/widgets/platform_button.dart';
 
 class ScanFilterWidget extends StatefulWidget {
-  final Function(ScanFilter? filter) onScanFilter;
+  final void Function(ScanFilter? filter) onScanFilter;
   final TextEditingController servicesFilterController;
   final TextEditingController namePrefixController;
   final TextEditingController manufacturerDataController;

example/lib/peripheral_details/widgets/result_widget.dart

@@ -3,7 +3,7 @@ import 'package:flutter/material.dart';
 class ResultWidget extends StatelessWidget {
   final List<String> results;
   final bool scrollable;
-  final Function(int? index) onClearTap;
+  final void Function(int? index) onClearTap;
   const ResultWidget({
     required this.results,
     required this.onClearTap,

example/lib/peripheral_details/widgets/services_list_widget.dart

@@ -5,7 +5,10 @@ import 'package:universal_ble/universal_ble.dart';
 class ServicesListWidget extends StatelessWidget {
   final List<BleService> discoveredServices;
   final bool scrollable;
-  final Function(BleService service, BleCharacteristic characteristic)? onTap;
+  final void Function(
+    BleService service,
+    BleCharacteristic characteristic,
+  )? onTap;
 
   const ServicesListWidget({
     super.key,

example/lib/widgets/platform_button.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 
 class PlatformButton extends StatelessWidget {
   final String text;
-  final Function()? onPressed;
+  final void Function()? onPressed;
   final bool enabled;
 
   const PlatformButton({