Initial Client/Server Communication

#1
Followed the MagicOnion quickstart guide, borrowing code from the chat sample app to get something working

Assets/Scripts/MessagePack/Formatters/NullableFormatter.cs

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+// Copyright (c) All contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Buffers;
+
+#pragma warning disable SA1649 // File name should match first type name
+
+namespace MessagePack.Formatters
+{
+    public sealed class NullableFormatter<T> : IMessagePackFormatter<T?>
+        where T : struct
+    {
+        public void Serialize(ref MessagePackWriter writer, T? value, MessagePackSerializerOptions options)
+        {
+            if (value == null)
+            {
+                writer.WriteNil();
+            }
+            else
+            {
+                options.Resolver.GetFormatterWithVerify<T>().Serialize(ref writer, value.Value, options);
+            }
+        }
+
+        public T? Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            if (reader.IsNil)
+            {
+                reader.ReadNil();
+                return null;
+            }
+            else
+            {
+                return options.Resolver.GetFormatterWithVerify<T>().Deserialize(ref reader, options);
+            }
+        }
+    }
+
+    public sealed class StaticNullableFormatter<T> : IMessagePackFormatter<T?>
+        where T : struct
+    {
+        private readonly IMessagePackFormatter<T> underlyingFormatter;
+
+        public StaticNullableFormatter(IMessagePackFormatter<T> underlyingFormatter)
+        {
+            this.underlyingFormatter = underlyingFormatter;
+        }
+
+        public void Serialize(ref MessagePackWriter writer, T? value, MessagePackSerializerOptions options)
+        {
+            if (value == null)
+            {
+                writer.WriteNil();
+            }
+            else
+            {
+                this.underlyingFormatter.Serialize(ref writer, value.Value, options);
+            }
+        }
+
+        public T? Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            if (reader.TryReadNil())
+            {
+                return null;
+            }
+            else
+            {
+                return this.underlyingFormatter.Deserialize(ref reader, options);
+            }
+        }
+    }
+}