Implement isScanning api (#188)

* Implement isScanning api

* Improve IOS scanning api

* Update Readme and Changelog

lib/src/universal_ble.dart

@@ -88,6 +88,14 @@ class UniversalBle {
     );
   }
 
+  /// Check if currently scanning for devices.
+  /// Returns `true` if scanning is active, `false` otherwise.
+  static Future<bool> isScanning() async {
+    return await _bleCommandQueue.queueCommand(
+      () => _platform.isScanning(),
+    );
+  }
+
   /// Connect to a device.
   /// It is advised to stop scanning before connecting.
   /// It throws error if device connection fails.

lib/src/universal_ble_linux/universal_ble_linux.dart

@@ -125,6 +125,12 @@ class UniversalBleLinux extends UniversalBlePlatform {
     }
   }
 
+  @override
+  Future<bool> isScanning() async {
+    await _ensureInitialized();
+    return _activeAdapter?.discovering == true;
+  }
+
   @override
   Future<BleConnectionState> getConnectionState(String deviceId) async {
     BlueZDevice? device = _devices[deviceId] ??

lib/src/universal_ble_pigeon/universal_ble.g.dart

@@ -1,4 +1,4 @@
-// Autogenerated from Pigeon (v26.0.5), do not edit directly.
+// Autogenerated from Pigeon (v26.1.0), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, prefer_null_aware_operators, omit_local_variable_types, unused_shown_name, unnecessary_import, no_leading_underscores_for_local_identifiers
 
@@ -633,6 +633,36 @@ class UniversalBlePlatformChannel {
     }
   }
 
+  Future<bool> isScanning() async {
+    final String pigeonVar_channelName =
+        'dev.flutter.pigeon.universal_ble.UniversalBlePlatformChannel.isScanning$pigeonVar_messageChannelSuffix';
+    final BasicMessageChannel<Object?> pigeonVar_channel =
+        BasicMessageChannel<Object?>(
+      pigeonVar_channelName,
+      pigeonChannelCodec,
+      binaryMessenger: pigeonVar_binaryMessenger,
+    );
+    final Future<Object?> pigeonVar_sendFuture = pigeonVar_channel.send(null);
+    final List<Object?>? pigeonVar_replyList =
+        await pigeonVar_sendFuture as List<Object?>?;
+    if (pigeonVar_replyList == null) {
+      throw _createConnectionError(pigeonVar_channelName);
+    } else if (pigeonVar_replyList.length > 1) {
+      throw PlatformException(
+        code: pigeonVar_replyList[0]! as String,
+        message: pigeonVar_replyList[1] as String?,
+        details: pigeonVar_replyList[2],
+      );
+    } else if (pigeonVar_replyList[0] == null) {
+      throw PlatformException(
+        code: 'null-error',
+        message: 'Host platform returned null value for non-null return value.',
+      );
+    } else {
+      return (pigeonVar_replyList[0] as bool?)!;
+    }
+  }
+
   Future<void> connect(String deviceId) async {
     final String pigeonVar_channelName =
         'dev.flutter.pigeon.universal_ble.UniversalBlePlatformChannel.connect$pigeonVar_messageChannelSuffix';

lib/src/universal_ble_pigeon/universal_ble_pigeon_channel.dart

@@ -57,6 +57,10 @@ class UniversalBlePigeonChannel extends UniversalBlePlatform {
   Future<void> stopScan() =>
       _executeWithErrorHandling(() => _channel.stopScan());
 
+  @override
+  Future<bool> isScanning() =>
+      _executeWithErrorHandling(() => _channel.isScanning());
+
   @override
   Future<BleConnectionState> getConnectionState(String deviceId) async {
     int state = await _executeWithErrorHandling(

lib/src/universal_ble_platform_interface.dart

@@ -43,6 +43,8 @@ abstract class UniversalBlePlatform {
 
   Future<void> stopScan();
 
+  Future<bool> isScanning();
+
   Future<void> connect(String deviceId, {Duration? connectionTimeout});
 
   Future<void> disconnect(String deviceId);

lib/src/universal_ble_web/universal_ble_web.dart

@@ -20,6 +20,7 @@ class UniversalBleWeb extends UniversalBlePlatform {
   final Map<String, StreamSubscription> _connectedDeviceStreamList = {};
   final Map<String, StreamSubscription> _characteristicStreamList = {};
   final Map<String, List<_UniversalWebBluetoothService>> _serviceCache = {};
+  bool _isScanning = false;
 
   @override
   Future<BleConnectionState> getConnectionState(String deviceId) async {
@@ -83,6 +84,7 @@ class UniversalBleWeb extends UniversalBlePlatform {
     PlatformConfig? platformConfig,
   }) async {
     try {
+      _isScanning = true;
       FlutterWebBluetooth.instance.isAvailable;
       BluetoothDevice device = await FlutterWebBluetooth.instance.requestDevice(
         _getRequestOptionBuilder(scanFilter, platformConfig?.web),
@@ -101,6 +103,8 @@ class UniversalBleWeb extends UniversalBlePlatform {
         throw WebBluetoothGloballyDisabled(message: error);
       }
       rethrow;
+    } finally {
+      _isScanning = false;
     }
   }
 
@@ -146,6 +150,9 @@ class UniversalBleWeb extends UniversalBlePlatform {
     _disposeAdvertisementWatcher();
   }
 
+  @override
+  Future<bool> isScanning() async => _isScanning;
+
   @override
   Future<void> setNotifiable(
     String deviceId,