Add ScribanRegistrationCallback to register custom Scriban functions (#1515) (#1516)

- Add WireMockServerSettings.ScribanRegistrationCallback
  (Action<object, IFileSystemHandler>?) so code-configured servers can add
  functions, objects or variables to Scriban and Scriban-DotLiquid templates.
- Pass the settings to ScribanContextFactory, which invokes the callback with
  a new ScriptObject per transformer context.
- Push the custom globals beneath the template model in ScribanContext so
  request, response, mapping and data take precedence; keep the original
  Template.Render call when no callback is configured.
- Add the strongly typed WithScribanRegistration extension method.
- Add a Scriban example to the .NET 8 console app.
- Make the proxy tests use a local target server instead of www.google.com,
  and skip the IPv6 loopback test when the OS has no IPv6 support.

Co-authored-by: Mattias <13809209+Quattordici@users.noreply.github.com>

examples/WireMock.Net.Console.NET8/MainApp.cs

@@ -3,6 +3,7 @@
 using System.Globalization;
 using System.Net;
 using Newtonsoft.Json;
+using Scriban.Runtime;
 using WireMock.Logging;
 using WireMock.Matchers;
 using WireMock.Models;
@@ -409,12 +410,26 @@ namespace WireMock.Net.ConsoleApplication
                     // handlebarsContext.RegisterHelper(transformer.Name, transformer.Render); TODO
                 },
 
+                ScribanRegistrationCallback = (scriptObject, fileSystemHandler) =>
+                {
+                    var globals = (ScriptObject)scriptObject;
+                    globals.Import("greet", new Func<string, string>(name => $"Hello {name}"));
+                },
+
                 // Uncomment below if you want to use the CustomFileSystemFileHandler
                 // FileSystemHandler = new CustomFileSystemFileHandler()
             });
             System.Console.WriteLine("WireMockServer listening at {0}", string.Join(",", server.Urls));
 
             server.SetBasicAuthentication("a", "b");
+
+            server
+                .Given(Request.Create().WithPath("/scriban/greet").UsingGet())
+                .RespondWith(Response.Create()
+                    .WithBody("{{ greet 'WireMock.Net' }}")
+                    .WithTransformer(TransformerType.Scriban)
+                );
+
             //server.SetAzureADAuthentication(Environment.GetEnvironmentVariable("WIREMOCK_AAD_TENANT")!, "api://e083d51a-01a6-446c-8ad5-0c5c7f002208");
 
             //var http = new HttpClient();