Port NBT impl from LibAC Dart

NBT/DoubleTag.cs

@@ -0,0 +1,67 @@
+using System;
+using LibAC.NBT.API;
+
+namespace LibAC.NBT
+{
+    public class DoubleTag : Tag
+    {
+        public double Value { get; private set; } = 0.0;
+
+        public DoubleTag() { }
+
+        private DoubleTag(double value)
+        {
+            Value = value;
+        }
+
+        public static DoubleTag ValueOf(double value)
+        {
+            return new DoubleTag(value);
+        }
+
+        public override void ReadValue(ByteLayer data)
+        {
+            Value = data.ReadDouble();
+        }
+
+        public override void WriteValue(ByteLayer data)
+        {
+            data.WriteDouble(Value);
+        }
+
+        public override TagType GetTagType()
+        {
+            return TagType.Double;
+        }
+
+        public override dynamic GetValue()
+        {
+            return Value;
+        }
+
+        public override void SetValue(dynamic val)
+        {
+            if (val is double)
+            {
+                Value = (double)val;
+            }
+        }
+
+        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}d");
+        }
+
+        public override void ReadStringifiedValue(StringReader reader)
+        {
+            double val = double.Parse(reader.ReadNumber());
+            Value = val;
+            reader.Expect('d');
+        }
+    }
+}