feat: Minor changes

lib/src/helpers.dart

@@ -86,9 +86,13 @@ extension BeforeAfterListDiff<T> on List<T> {
 
 extension AppendToListOrCreateExtension<K, V> on Map<K, List<V>> {
   /// Create or append [value] to the list identified with key [key].
-  void appendOrCreate(K key, V value) {
+  void appendOrCreate(K key, V value, {bool checkExistence = false}) {
     if (containsKey(key)) {
-      this[key]!.add(value);
+      if (!checkExistence) {
+        this[key]!.add(value);
+      } if (!this[key]!.contains(value)) {
+        this[key]!.add(value);
+      }
     } else {
       this[key] = [value];
     }

lib/src/trust/btbv.dart

@@ -132,11 +132,8 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
       enablementCache[key] = true;
     }
 
-    if (devices.containsKey(jid)) {
-      devices[jid]!.add(deviceId);
-    } else {
-      devices[jid] = List<int>.from([deviceId]);
-    }
+    // Append to the device list
+    devices.appendOrCreate(jid, deviceId, checkExistence: true);
 
     // Commit the state
     await commit(
@@ -227,7 +224,7 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
       final key = RatchetMapKey(jid, result.device);
       trustCache[key] = result.state;
       enablementCache[key] = result.enabled;
-      devices.appendOrCreate(jid, result.device);
+      devices.appendOrCreate(jid, result.device, checkExistence: true);
     }
   }