rename MessageSerializer to ApiMessageSerializer

Pilz.Net/Api/ApiMessageHandlerAttribute.cs

@@ -0,0 +1,9 @@
+namespace Pilz.Net.Api;
+
+[AttributeUsage(AttributeTargets.Method)]
+public class ApiMessageHandlerAttribute(string route) : Attribute
+{
+    public string Route { get; set; } = route;
+    public Type? Serializer { get; set; }
+    public bool RequiesAuth { get; set; }
+}