fix: Migrate to custom protobuf

lib/src/protobuf/omemo_authenticated_message.dart

@@ -3,7 +3,7 @@ import 'package:omemo_dart/src/protobuf/protobuf.dart';
 
 class OmemoAuthenticatedMessage {
 
-  const OmemoAuthenticatedMessage(this.mac, this.message);
+  OmemoAuthenticatedMessage();
 
   factory OmemoAuthenticatedMessage.fromBuffer(List<int> data) {
     var i = 0;
@@ -20,18 +20,20 @@ class OmemoAuthenticatedMessage {
     }
     final message = data.sublist(i + 2, i + 2 + data[i + 1]);
 
-    return OmemoAuthenticatedMessage(mac, message);
+    return OmemoAuthenticatedMessage()
+      ..mac = mac
+      ..message = message;
   }
   
-  final List<int> mac;
-  final List<int> message;
+  List<int>? mac;
+  List<int>? message;
 
   List<int> writeToBuffer() {
     return concat([
-      [fieldId(1, fieldTypeByteArray), mac.length],
-      mac,
-      [fieldId(2, fieldTypeByteArray), message.length],
-      message,
+      [fieldId(1, fieldTypeByteArray), mac!.length],
+      mac!,
+      [fieldId(2, fieldTypeByteArray), message!.length],
+      message!,
     ]);
   }
 }

lib/src/protobuf/omemo_key_exchange.dart

@@ -4,7 +4,7 @@ import 'package:omemo_dart/src/protobuf/protobuf.dart';
 
 class OmemoKeyExchange {
 
-  const OmemoKeyExchange(this.pkId, this.spkId, this.ik, this.ek, this.message);
+  OmemoKeyExchange();
 
   factory OmemoKeyExchange.fromBuffer(List<int> data) {
     var i = 0;
@@ -40,26 +40,31 @@ class OmemoKeyExchange {
     }
     final message = OmemoAuthenticatedMessage.fromBuffer(data.sublist(i + 2));
 
-    return OmemoKeyExchange(pkId, spkId, ik, ek, message);
+    return OmemoKeyExchange()
+      ..pkId = pkId
+      ..spkId = spkId
+      ..ik = ik
+      ..ek = ek
+      ..message = message;
   }
   
-  final int pkId;
-  final int spkId;
-  final List<int> ik;
-  final List<int> ek;
-  final OmemoAuthenticatedMessage message;
+  int? pkId;
+  int? spkId;
+  List<int>? ik;
+  List<int>? ek;
+  OmemoAuthenticatedMessage? message;
 
   List<int> writeToBuffer() {
-    final msg = message.writeToBuffer();
+    final msg = message!.writeToBuffer();
     return concat([
       [fieldId(1, fieldTypeUint32)],
-      encodeVarint(pkId),
+      encodeVarint(pkId!),
       [fieldId(2, fieldTypeUint32)],
-      encodeVarint(spkId),
-      [fieldId(3, fieldTypeByteArray), ik.length],
-      ik,
-      [fieldId(4, fieldTypeByteArray), ek.length],
-      ek,
+      encodeVarint(spkId!),
+      [fieldId(3, fieldTypeByteArray), ik!.length],
+      ik!,
+      [fieldId(4, fieldTypeByteArray), ek!.length],
+      ek!,
       [fieldId(5, fieldTypeByteArray), msg.length],
       msg,
     ]);

lib/src/protobuf/omemo_message.dart

@@ -3,7 +3,7 @@ import 'package:omemo_dart/src/protobuf/protobuf.dart';
 
 class OmemoMessage {
 
-  const OmemoMessage(this.n, this.pn, this.dhPub, this.ciphertext);
+  OmemoMessage();
 
   factory OmemoMessage.fromBuffer(List<int> data) {
     var i = 0;
@@ -41,28 +41,32 @@ class OmemoMessage {
       ciphertext = data.sublist(i + 2, i + 2 + data[i + 1]);
     }
 
-    return OmemoMessage(n, pn, dhPub, ciphertext);
+    return OmemoMessage()
+      ..n = n
+      ..pn = pn
+      ..dhPub = dhPub
+      ..ciphertext = ciphertext;
   }
 
-  final int n;
-  final int pn;
-  final List<int> dhPub;
-  final List<int>? ciphertext;
+  int? n;
+  int? pn;
+  List<int>? dhPub;
+  List<int>? ciphertext;
 
   List<int> writeToBuffer() {
     final data = concat([
-      [8],
-      encodeVarint(n),
-      [16],
-      encodeVarint(pn),
-      [((3 << 3) | 2), dhPub.length],
-      dhPub,
+      [fieldId(1, fieldTypeUint32)],
+      encodeVarint(n!),
+      [fieldId(2, fieldTypeUint32)],
+      encodeVarint(pn!),
+      [fieldId(3, fieldTypeByteArray), dhPub!.length],
+      dhPub!,
     ]);
 
     if (ciphertext != null) {
       return concat([
         data,
-        [((4 << 3) | 2), ciphertext!.length],
+        [fieldId(4, fieldTypeByteArray), ciphertext!.length],
         ciphertext!,
       ]);
     }