feat: Implement all protobuf messages

lib/src/protobuf/omemo_authenticated_message.dart

@@ -0,0 +1,37 @@
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+
+class OmemoAuthenticatedMessage {
+
+  const OmemoAuthenticatedMessage(this.mac, this.message);
+
+  factory OmemoAuthenticatedMessage.fromBuffer(List<int> data) {
+    var i = 0;
+    
+    // required bytes mac     = 1;
+    if (data[0] != fieldId(1, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final mac = data.sublist(2, i + 2 + data[1]);
+    i += data[1] + 2;
+
+    if (data[i] != fieldId(2, fieldTypeByteArray)) {
+      throw Exception();
+    }
+    final message = data.sublist(i + 2, i + 2 + data[i + 1]);
+
+    return OmemoAuthenticatedMessage(mac, message);
+  }
+  
+  final List<int> mac;
+  final List<int> message;
+
+  List<int> writeToBuffer() {
+    return concat([
+      [fieldId(1, fieldTypeByteArray), mac.length],
+      mac,
+      [fieldId(2, fieldTypeByteArray), message.length],
+      message,
+    ]);
+  }
+}