Port NBT impl from LibAC Dart

NBT/LongTag.cs

@@ -0,0 +1,65 @@
+using System;
+using LibAC.NBT.API;
+
+namespace LibAC.NBT
+{
+    public class LongTag : Tag
+    {
+        public long value { get; private set; } = 0;
+
+        public LongTag() { }
+
+        public LongTag(long value)
+        {
+            this.value = value;
+        }
+
+        public static LongTag ValueOf(long value)
+        {
+            return new LongTag(value);
+        }
+
+        public override void ReadValue(ByteLayer data)
+        {
+            value = data.ReadLong();
+        }
+
+        public override void WriteValue(ByteLayer data)
+        {
+            data.WriteLong(value);
+        }
+
+        public override TagType GetTagType()
+        {
+            return TagType.Long;
+        }
+
+        public override void SetValue(dynamic val)
+        {
+            if (val is long) value = val;
+        }
+
+        public override dynamic GetValue()
+        {
+            return value;
+        }
+
+        public override void PrettyPrint(int indent, bool recurse)
+        {
+            Console.WriteLine($"{new string('\t', indent)}{Tag.GetCanonicalName(GetTagType())}: {value}");
+        }
+
+        public override void WriteStringifiedValue(StringBuilder builder, int indent, bool isList)
+        {
+            builder.Append($"{(isList ? new string('\t', indent) : "")}{value}L");
+        }
+
+        public override void ReadStringifiedValue(StringReader reader)
+        {
+            long val = long.Parse(reader.ReadNumber());
+            value = val;
+
+            reader.Expect('l');
+        }
+    }
+}