Port NBT impl from LibAC Dart

NBT/API/NbtUUID.cs

@@ -0,0 +1,43 @@
+using System;
+using LibAC.Utilities;
+
+namespace LibAC.NBT.API
+{
+    public class NbtUUID
+    {
+        public long MSB { get; }
+        public long LSB { get; }
+
+        public static readonly NbtUUID ZERO = new NbtUUID(UUID.ZERO);
+
+        public NbtUUID(long msb, long lsb)
+        {
+            MSB = msb;
+            LSB = lsb;
+        }
+
+        public NbtUUID(UUID uuid)
+        {
+            byte[] uuidBytes = uuid.GetBytes();
+            MSB = BitConverter.ToInt64(uuidBytes, 0);
+            LSB = BitConverter.ToInt64(uuidBytes, 8);
+        }
+
+        public long GetMostSignificantBits() => MSB;
+
+        public long GetLeastSignificantBits() => LSB;
+
+        public UUID ToUUID()
+        {
+            byte[] bytes = new byte[16];
+            BitConverter.GetBytes(MSB).CopyTo(bytes, 0);
+            BitConverter.GetBytes(LSB).CopyTo(bytes, 8);
+            return new UUID(bytes);
+        }
+
+        public override string ToString()
+        {
+            return ToUUID().ToString();
+        }
+    }
+}