fixup! chore(core): make createClient async

Author: JKRhb

test/binding_coap/binding_coap_test.dart

@@ -50,9 +50,9 @@ void main() {
       expect(defaultClientFactory.coapConfig, null);
       expect(defaultClientFactory.init(), true);
 
+      final coapClient = await defaultClientFactory.createClient();
 
       await coapClient.start();
-      final coapClient = await defaultClientFactory.createClient();
 
       await coapClient.stop();