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/UnsafeBinaryFormatters.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;
+using System.Buffers;
+
+#pragma warning disable SA1649 // File name should match first type name
+
+namespace MessagePack.Formatters
+{
+    public sealed class NativeGuidFormatter : IMessagePackFormatter<Guid>
+    {
+        /// <summary>
+        /// Unsafe binary Guid formatter. this is only allowed on LittleEndian environment.
+        /// </summary>
+        public static readonly IMessagePackFormatter<Guid> Instance = new NativeGuidFormatter();
+
+        private NativeGuidFormatter()
+        {
+        }
+
+        /* Guid's underlying _a,...,_k field is sequential and same layout as .NET Framework and Mono(Unity).
+         * But target machines must be same endian so restrict only for little endian. */
+
+        public unsafe void Serialize(ref MessagePackWriter writer, Guid value, MessagePackSerializerOptions options)
+        {
+            if (!BitConverter.IsLittleEndian)
+            {
+                throw new InvalidOperationException("NativeGuidFormatter only allows on little endian env.");
+            }
+
+            var valueSpan = new ReadOnlySpan<byte>(&value, sizeof(Guid));
+            writer.Write(valueSpan);
+        }
+
+        public unsafe Guid Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            if (!BitConverter.IsLittleEndian)
+            {
+                throw new InvalidOperationException("NativeGuidFormatter only allows on little endian env.");
+            }
+
+            ReadOnlySequence<byte> valueSequence = reader.ReadBytes().Value;
+            if (valueSequence.Length != sizeof(Guid))
+            {
+                throw new MessagePackSerializationException("Invalid Guid Size.");
+            }
+
+            Guid result;
+            var resultSpan = new Span<byte>(&result, sizeof(Guid));
+            valueSequence.CopyTo(resultSpan);
+            return result;
+        }
+    }
+
+    public sealed class NativeDecimalFormatter : IMessagePackFormatter<Decimal>
+    {
+        /// <summary>
+        /// Unsafe binary Decimal formatter. this is only allows on LittleEndian environment.
+        /// </summary>
+        public static readonly IMessagePackFormatter<Decimal> Instance = new NativeDecimalFormatter();
+
+        private NativeDecimalFormatter()
+        {
+        }
+
+        /* decimal underlying "flags, hi, lo, mid" fields are sequential and same layuout with .NET Framework and Mono(Unity)
+         * But target machines must be same endian so restrict only for little endian. */
+
+        public unsafe void Serialize(ref MessagePackWriter writer, Decimal value, MessagePackSerializerOptions options)
+        {
+            if (!BitConverter.IsLittleEndian)
+            {
+                throw new InvalidOperationException("NativeDecimalFormatter only allows on little endian env.");
+            }
+
+            var valueSpan = new ReadOnlySpan<byte>(&value, sizeof(Decimal));
+            writer.Write(valueSpan);
+        }
+
+        public unsafe Decimal Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            if (!BitConverter.IsLittleEndian)
+            {
+                throw new InvalidOperationException("NativeDecimalFormatter only allows on little endian env.");
+            }
+
+            ReadOnlySequence<byte> valueSequence = reader.ReadBytes().Value;
+            if (valueSequence.Length != sizeof(decimal))
+            {
+                throw new MessagePackSerializationException("Invalid decimal Size.");
+            }
+
+            decimal result;
+            var resultSpan = new Span<byte>(&result, sizeof(decimal));
+            valueSequence.CopyTo(resultSpan);
+            return result;
+        }
+    }
+}