fix: Make decryption work

test/omemo_test.dart

@@ -0,0 +1,69 @@
+import 'dart:convert';
+import 'package:omemo_dart/omemo_dart.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('Test using OMEMO sessions with only one device per user', () async {
+    const aliceJid = 'alice@server.example';
+    const bobJid = 'bob@other.server.example';
+      
+    // Alice and Bob generate their sessions
+    final aliceSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+    final bobSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+
+    // Perform the X3DH
+    final x3dhAliceResult = await x3dhFromBundle(
+      await bobSession.device.toBundle(),
+      aliceSession.device.ik,
+    );
+    final x3dhBobResult = await x3dhFromInitialMessage(
+      X3DHMessage(
+        aliceSession.device.ik.pk,
+        x3dhAliceResult.ek.pk,
+        '2',
+      ),
+      bobSession.device.spk,
+      bobSession.device.opks.values.elementAt(0),
+      bobSession.device.ik,
+    );
+
+    // Build the ratchets
+    final aliceRatchet = await OmemoDoubleRatchet.initiateNewSession(
+      bobSession.device.spk.pk,
+      x3dhAliceResult.sk,
+      x3dhAliceResult.ad,
+    );
+    final bobRatchet = await OmemoDoubleRatchet.acceptNewSession(
+      bobSession.device.spk,
+      x3dhBobResult.sk,
+      x3dhBobResult.ad,
+    );
+
+    // Add the ratchets to the session managers
+    await aliceSession.addSession(bobJid, bobSession.device.id, aliceRatchet);
+    await bobSession.addSession(aliceJid, aliceSession.device.id, bobRatchet);
+
+    // Alice encrypts a message for Bob
+    const messagePlaintext = 'Hello Bob!';
+    final aliceMessage = await aliceSession.encryptToJid(bobJid, messagePlaintext);
+    expect(aliceMessage.encryptedKeys.length, 1);
+
+    // Alice sends the message to Bob
+    // ...
+
+    // Bob decrypts it
+    final bobMessage = await bobSession.decryptMessage(
+      aliceMessage.ciphertext,
+      aliceJid,
+      aliceSession.device.id,
+      [
+        EncryptedKey(
+          bobSession.device.id,
+          base64.encode(aliceMessage.encryptedKeys[bobSession.device.id]!),
+        ),
+      ],
+    );
+
+    expect(messagePlaintext, bobMessage);
+  });
+}