fix: Fix receiving an old key exchange breaking decryption

This was mostly caused by Dart not copying values but referencing
them. AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.

We know make some assumptions about received key exchanges, so this
needs some field testing.

test/double_ratchet_test.dart

@@ -84,6 +84,7 @@ void main() {
       ikBob.pk,
       resultAlice.sk,
       resultAlice.ad,
+      0,
     );
     final bobsRatchet = await OmemoDoubleRatchet.acceptNewSession(
       spkBob,

test/omemo_test.dart

@@ -653,7 +653,7 @@ void main() {
     expect(await bobRatchet1.equals(bobRatchet2), false);
   });
 
-  test('Test receiving an old message that contains a KEX', () async {
+  test('Test receiving old messages including a KEX', () async {
     const aliceJid = 'alice@server.example';
     const bobJid = 'bob@other.server.example';
     // Alice and Bob generate their sessions
@@ -668,6 +668,8 @@ void main() {
       opkAmount: 2,
     );
 
+    final bobsReceivedMessages = List<EncryptionResult>.empty(growable: true);
+    
     // Alice sends Bob a message
     final msg1 = await aliceSession.encryptToJid(
       bobJid,
@@ -676,7 +678,7 @@ void main() {
         await bobSession.getDeviceBundle(),
       ],
     );
-
+    bobsReceivedMessages.add(msg1);
     await bobSession.decryptMessage(
       msg1.ciphertext,
       aliceJid,
@@ -696,90 +698,51 @@ void main() {
       msg2.encryptedKeys,
     );
 
-    // Due to some issue with the transport protocol, the first message Bob received is
-    // received again
-    try {
-      await bobSession.decryptMessage(
-        msg1.ciphertext,
+    // Send some messages between the two
+    for (var i = 0; i < 100; i++) {
+      final msg = await aliceSession.encryptToJid(
+        bobJid,
+        'Hello $i',
+      );
+      bobsReceivedMessages.add(msg);
+      final result = await bobSession.decryptMessage(
+        msg.ciphertext,
         aliceJid,
         await aliceSession.getDeviceId(),
-        msg1.encryptedKeys,
+        msg.encryptedKeys,
       );
-      expect(true, false);
-    } on InvalidMessageHMACException {
-      // NOOP
+
+      expect(result, 'Hello $i');
     }
 
-    final msg3 = await aliceSession.encryptToJid(
-      bobJid,
-      'Are you okay?',
-    );
-    final result = await bobSession.decryptMessage(
-      msg3.ciphertext,
-      aliceJid,
-      await aliceSession.getDeviceId(),
-      msg3.encryptedKeys,
-    );
-
-    expect(result, 'Are you okay?');
-  });
-
-  test('Test receiving an old message that does not contain a KEX', () async {
-    const aliceJid = 'alice@server.example';
-    const bobJid = 'bob@other.server.example';
-    // Alice and Bob generate their sessions
-    final aliceSession = await OmemoSessionManager.generateNewIdentity(
-      aliceJid,
-      AlwaysTrustingTrustManager(),
-      opkAmount: 1,
-    );
-    final bobSession = await OmemoSessionManager.generateNewIdentity(
-      bobJid,
-      AlwaysTrustingTrustManager(),
-      opkAmount: 2,
-    );
-
-    // Alice sends Bob a message
-    final msg1 = await aliceSession.encryptToJid(
-      bobJid,
-      'Hallo Welt',
-      newSessions: [
-        await bobSession.getDeviceBundle(),
-      ],
-    );
-    await bobSession.decryptMessage(
-      msg1.ciphertext,
-      aliceJid,
-      await aliceSession.getDeviceId(),
-      msg1.encryptedKeys,
-    );
-
-    // Bob responds
-    final msg2 = await bobSession.encryptToJid(
-      aliceJid,
-      'Hello!',
-    );
-    await aliceSession.decryptMessage(
-      msg2.ciphertext,
-      bobJid,
-      await bobSession.getDeviceId(),
-      msg2.encryptedKeys,
-    );
-
-    // Due to some issue with the transport protocol, the first message Alice received is
-    // received again.
-    try {
-      await aliceSession.decryptMessage(
-        msg2.ciphertext,
-        bobJid,
-        await bobSession.getDeviceId(),
-        msg2.encryptedKeys,
-      );
-      expect(true, false);
-    } catch (_) {
-      // NOOP
+    // Due to some issue with the transport protocol, the messages to Bob are received
+    // again.
+    final ratchetPreError = bobSession
+      .getRatchet(aliceJid, await aliceSession.getDeviceId())
+      .clone();
+    var errorCounter = 0;
+    for (final msg in bobsReceivedMessages) {
+      try {
+        await bobSession.decryptMessage(
+          msg.ciphertext,
+          aliceJid,
+          await aliceSession.getDeviceId(),
+          msg.encryptedKeys,
+        );
+        expect(true, false);
+      } catch (_) {
+        errorCounter++;
+      }
     }
+    final ratchetPostError = bobSession
+      .getRatchet(aliceJid, await aliceSession.getDeviceId())
+      .clone();
 
+    // The 100 messages including the initial KEX message
+    expect(errorCounter, 101);
+    expect(await ratchetPreError.equals(ratchetPostError), true);
+
+    
     final msg3 = await aliceSession.encryptToJid(
       bobJid,
       'Are you okay?',

test/serialisation_test.dart

@@ -86,6 +86,7 @@ void main() {
       'bob@localhost',
       await bobSession.getDeviceId(),
       await bobSession.getDeviceBundle(),
+      0,
     );
 
     // Serialise and deserialise