fix(core): cache XML serializers

SharedCode.Core/Xml/XDocumentExtensions.cs

@@ -8,6 +8,11 @@ namespace SharedCode.Xml;
 /// </summary>
 public static class XDocumentExtensions
 {
+	/// <summary>
+	/// Cached XML serializers by runtime type.
+	/// </summary>
+	private static readonly Dictionary<RuntimeTypeHandle, XmlSerializer> XmlSerializers = [];
+
 	/// <summary>
 	/// Deserializes the specified XML document.
 	/// </summary>
@@ -19,8 +24,37 @@ public static class XDocumentExtensions
 	{
 		_ = xmlDocument ?? throw new ArgumentNullException(nameof(xmlDocument));
 
-		var xmlSerializer = new XmlSerializer(typeof(T));
+		var xmlSerializer = GetXmlSerializer(typeof(T));
 		using var reader = xmlDocument.CreateReader();
 		return (T?)xmlSerializer.Deserialize(reader);
 	}
+
+	/// <summary>
+	/// Gets the XML serializer for the specified <paramref name="type" />.
+	/// </summary>
+	/// <param name="type">The type handled by the serializer.</param>
+	/// <returns>The <see cref="XmlSerializer" /> for the <paramref name="type" />.</returns>
+	/// <exception cref="ArgumentNullException">type</exception>
+	private static XmlSerializer GetXmlSerializer(Type type)
+	{
+		_ = type ?? throw new ArgumentNullException(nameof(type));
+
+		if (XmlSerializers.TryGetValue(type.TypeHandle, out var serializer))
+		{
+			return serializer;
+		}
+
+		lock (XmlSerializers)
+		{
+			if (XmlSerializers.TryGetValue(type.TypeHandle, out serializer))
+			{
+				return serializer;
+			}
+
+			serializer = new XmlSerializer(type);
+			XmlSerializers.Add(type.TypeHandle, serializer);
+		}
+
+		return serializer;
+	}
 }