feat: Allow serialising Device to Json

test/serialisation_test.dart

@@ -0,0 +1,24 @@
+import 'package:omemo_dart/omemo_dart.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('Test serialising and deserialising Device', () async {
+    // Generate a random session
+    final oldSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+    final oldDevice = await oldSession.getDevice();
+    final serialised = await oldDevice.toJson();
+
+    final newDevice = Device.fromJson(serialised);
+    expect(oldDevice.id, newDevice.id);
+    expect(await oldDevice.ik.equals(newDevice.ik), true);
+    expect(await oldDevice.spk.equals(newDevice.spk), true);
+    expect(listsEqual(oldDevice.spkSignature, newDevice.spkSignature), true);
+    expect(oldDevice.spkId, newDevice.spkId);
+
+    // Check the Ontime-Prekeys
+    expect(oldDevice.opks.length, newDevice.opks.length);
+    for (final entry in oldDevice.opks.entries) {
+      expect(await newDevice.opks[entry.key]!.equals(entry.value), true);
+    }
+  });
+}