fix: [native] Fix errors when hot restarted

[littleGnAl]

Fix errors when hot started

1. Type cast error

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'Pointer<NativeType>' is not a subtype of type 'Pointer<Void>' in type cast
#0      NativeIrisApiEngineBindingsDelegate.destroyNativeApiEngine (package:agora_rtc_engine/src/impl/platform/io/native_iris_api_engine_binding_delegate.dart:167:50)
#1      _HotRestartFinalizer._finalize (package:iris_method_channel/src/platform/io/iris_method_channel_internal_io.dart:152:27)
#2      _RootZone.runUnaryGuarded (dart:async/zone.dart:1586:10)
#3      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)
#4      _BufferingStreamSubscription._add (dart:async/stream_impl.dart:271:7)
#5      _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:774:19)
#6      _StreamController._add (dart:async/stream_controller.dart:648:7)
#7      _StreamController.add (dart:async/stream_controller.dart:596:5)
#8      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:192:12)

2. The provideIrisEvent assertion error

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: 'package:iris_method_channel/src/platform/io/iris_method_channel_internal_io.dart': Failed assertion: line 161 pos 12: 'provider.provideIrisEvent() != null': is not true.
#0      _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:51:61)
#1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:40:5)
#2      _HotRestartFinalizer._finalize (package:iris_method_channel/src/platform/io/iris_method_channel_internal_io.dart:161:12)
#3      _RootZone.runUnaryGuarded (dart:async/zone.dart:1586:10)
#4      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)
#5      _BufferingStreamSubscription._add (dart:async/stream_impl.dart:271:7)
#6      _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:774:19)
#7      _StreamController._add (dart:async/stream_controller.dart:648:7)
#8      _StreamController.add (dart:async/stream_controller.dart:596:5)
#9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:192:12)