avoid extra allocs in serializing commands, update example

example/console/example.dart

@@ -8,12 +8,18 @@ void main() async {
   final channel = 'chat:index';
   // generate user JWT token for user "dart":
   // ./centrifugo gentoken --user dart
+  // For this example we generated token using HMAC secret key "secret". Don't forget
+  // that it's just an example, and tokens never should be generated on client side and
+  // HMAC secret revealed to client side.
   final userJwtToken =
-      'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJkYXJ0IiwiZXhwIjoyMjc5NDQzNjgwLCJpYXQiOjE2NzQ2NDM2ODB9.XgsPZzAD4kMj7HdybJfpMGuDaRmuLvhUUxCGHs3mtXA';
+      'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJkYXJ0IiwiaWF0IjoxNzM3ODAwOTcxfQ.m30QzH9nxqMSJw3g5gL5Tjqnu-veQSn4RcH47ZozqQI';
   // generate subscription JWT token for user "dart" and channel "chat:index":
   // ./centrifugo gensubtoken --user dart --channel chat:index
+  // For this example we generated subscription token using HMAC secret key "secret". Don't forget
+  // that it's just an example, and tokens never should be generated on client side and
+  // HMAC secret revealed to client side.
   final subscriptionJwtToken =
-      'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJkYXJ0IiwiZXhwIjoyMjc5NDQ0MDE4LCJpYXQiOjE2NzQ2NDQwMTgsImNoYW5uZWwiOiJjaGF0OmluZGV4In0.FjpnF6ofq3XCr1iqnwTZcpxCx6btuzCnn29DAIJbsBo';
+      'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJkYXJ0IiwiaWF0IjoxNzM3ODAxMDIwLCJjaGFubmVsIjoiY2hhdDppbmRleCJ9.fe3WguZKkGiTyacpUW-WJW-1yzpZTHAFO6FWo7gbbTs';
 
   final onEvent = (dynamic event) {
     print('client> $event');

lib/src/codec.dart

@@ -11,12 +11,11 @@ class ProtobufCommandEncoder extends CommandEncoder {
   @override
   List<int> convert(Command input) {
     final commandData = input.writeToBuffer();
-    final length = commandData.lengthInBytes;
 
-    final writer = CodedBufferWriter();
-    writer.writeInt32NoTag(length);
-
-    return writer.toBuffer() + commandData;
+    return (CodedBufferWriter()
+          ..writeInt32NoTag(commandData.length)
+          ..writeRawBytes(commandData))
+        .toBuffer();
   }
 }