Corrected UniqueId implementation.

Thanks @Anaminus!

DataTypes/UniqueId.cs

@@ -0,0 +1,16 @@
+namespace RobloxFiles.DataTypes
+{
+    public struct UniqueId
+    {
+        public readonly uint Time;
+        public readonly uint Index;
+        public readonly ulong Random;
+
+        public UniqueId(uint time, uint index, ulong random)
+        {
+            Time = time;
+            Index = index;
+            Random = random;
+        }
+    }
+}