Implement market board purchase message reading

Originally from d85146c0d9

Dalamud/Game/Network/Structures/MarketBoardPurchase.cs

@@ -0,0 +1,40 @@
+using System;
+using System.IO;
+
+namespace Dalamud.Game.Network.Structures
+{
+    /// <summary>
+    /// Represents market board purchase information. This message is received from the
+    /// server when a purchase is made at a market board.
+    /// </summary>
+    internal class MarketBoardPurchase
+    {
+        /// <summary>
+        /// Gets the item ID of the item that was purchased.
+        /// </summary>
+        public uint CatalogId { get; private set; }
+
+        /// <summary>
+        /// Gets the quantity of the item that was purchased.
+        /// </summary>
+        public uint ItemQuantity { get; private set; }
+
+        /// <summary>
+        /// Reads market board purchase information from the struct at the provided pointer.
+        /// </summary>
+        /// <param name="dataPtr">A pointer to a struct containing market board purchase information from the server.</param>
+        /// <returns>An object representing the data read.</returns>
+        public static unsafe MarketBoardPurchase Read(IntPtr dataPtr)
+        {
+            var output = new MarketBoardPurchase();
+
+            using var stream = new UnmanagedMemoryStream((byte*)dataPtr.ToPointer(), 1544);
+            using var reader = new BinaryReader(stream);
+            output.CatalogId = reader.ReadUInt32();
+            stream.Position += 4;
+            output.ItemQuantity = reader.ReadUInt32();
+
+            return output;
+        }
+    }
+}