feat: add support for Duration type

By default, BclTicks (100ns) representation is used. Provides also a Nanosecond precision as opt-in.

resolves: #19

MessagePack.NodaTime.Tests/NodaTimeTests/DurationMessagePackFormatterTest.cs

@@ -0,0 +1,32 @@
+// Copyright (c) ARK LTD. All rights reserved.
+// Licensed under the MIT License. See LICENSE in the project root for
+// license information. 
+using MessagePack.NodaTime.Tests.Helpers;
+using NodaTime;
+using System;
+using Xunit;
+
+namespace MessagePack.NodaTime.Tests
+{
+    [Collection("ResolverCollection")]
+    public class DurationMessagePackFormatterTest
+    {
+        [Fact]
+        public void DurationTest()
+        {
+            var d = Duration.FromDays(1);
+            Assert.Equal(TestTools.Convert(d), d);
+        }
+
+        [Fact]
+        public void DurationArrayTest()
+        {
+            var p = new Duration[]
+            { 
+                Duration.FromDays(1),
+                Duration.FromNanoseconds(100),
+            };
+            Assert.Equal(TestTools.Convert(p), p);
+        }
+    }
+}

MessagePack.NodaTime/DurationMessagePackFormatter.cs

@@ -0,0 +1,46 @@
+// Copyright (c) ARK LTD. All rights reserved.
+// Licensed under the MIT License. See LICENSE in the project root for
+// license information. 
+using MessagePack.Formatters;
+
+using NodaTime;
+using NodaTime.Text;
+
+using System;
+
+namespace MessagePack.NodaTime
+{
+    public sealed class DurationAsNanosecondsMessagePackFormatter : IMessagePackFormatter<Duration>
+    {
+        public static readonly DurationAsNanosecondsMessagePackFormatter Instance = new DurationAsNanosecondsMessagePackFormatter();
+
+        public Duration Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            var s = reader.ReadInt64();
+
+            return Duration.FromNanoseconds(s);
+        }
+
+        public void Serialize(ref MessagePackWriter writer, Duration value, MessagePackSerializerOptions options)
+        {
+            writer.Write(value.ToInt64Nanoseconds());
+        }
+    }
+
+    public sealed class DurationAsBclTicksMessagePackFormatter : IMessagePackFormatter<Duration>
+    {
+        public static readonly DurationAsBclTicksMessagePackFormatter Instance = new DurationAsBclTicksMessagePackFormatter();
+
+        public Duration Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            var s = reader.ReadInt64();
+
+            return Duration.FromTicks(s);
+        }
+
+        public void Serialize(ref MessagePackWriter writer, Duration value, MessagePackSerializerOptions options)
+        {
+            writer.Write(value.BclCompatibleTicks);
+        }
+    }
+}

MessagePack.NodaTime/NodatimeResolver.cs

@@ -44,6 +44,7 @@ internal static class NodatimeResolverGetFormatterHelper
 
             {typeof(Offset), OffsetMessagePackFormatter.Instance},
             {typeof(Period), PeriodAsIntArrayMessagePackFormatter.Instance},
+            {typeof(Duration), DurationAsBclTicksMessagePackFormatter.Instance },
 
             {typeof(OffsetDateTime), OffsetDateTimeMessagePackFormatter.Instance},
             {typeof(ZonedDateTime), ZonedDateTimeMessagePackFormatter.Instance},
@@ -55,6 +56,7 @@ internal static class NodatimeResolverGetFormatterHelper
             {typeof(Offset?), new NullableFormatter<Offset>() },
             {typeof(OffsetDateTime?), new NullableFormatter<OffsetDateTime>() },
             {typeof(ZonedDateTime?), new NullableFormatter<ZonedDateTime>() },
+            {typeof(Duration?), new NullableFormatter<Duration>() },
         };
 
         internal static object? GetFormatter(Type t)