🐛 Fix balance value not being of type double

lib/mixer_state.dart

@@ -83,7 +83,7 @@ class State {
   String? toUuid;
   bool mute;
   double volume;
-  int balance;
+  double balance;
 
   State({
     this.toUuid,
@@ -96,7 +96,7 @@ class State {
         toUuid: json["toUUID"],
         mute: json["mute"],
         volume: json["volume"]?.toDouble(),
-        balance: json["balance"],
+        balance: json["balance"]?.toDouble(),
       );
 
   Map<String, dynamic> toJson() => {