[Quattordici]

Fixes #1515

Before

Handlebars templates could be extended with custom helpers through WireMockServerSettings.HandlebarsRegistrationCallback, but Scriban and Scriban-DotLiquid templates had no way to add custom functions.

After

WireMockServerSettings.ScribanRegistrationCallback (Action<object, IFileSystemHandler>?) lets code-configured servers add functions, objects or variables to a Scriban ScriptObject. Those members are available in both TransformerType.Scriban and TransformerType.ScribanDotLiquid templates, for responses, webhooks, proxy URL replacement and WebSockets.

var settings = new WireMockServerSettings
{
    ScribanRegistrationCallback = (scriptObject, fileSystemHandler) =>
        ((ScriptObject)scriptObject).Import("fake_name", new Func<string>(() => "Jane Doe"))
};

// or, strongly typed:
settings.WithScribanRegistration((scriptObject, fileSystemHandler) =>
    scriptObject.Import("fake_name", new Func<string>(() => "Jane Doe")));

The first argument is a Scriban.Runtime.ScriptObject from Scriban.Signed. It is typed as object so that WireMock.Net.Shared does not depend on Scriban. The registered globals sit beneath the template model, so request, response, mapping and data always win on a name clash. Template assignments write to the model scope and never change the registered globals.

How

• WireMockServerSettings gets the new ScribanRegistrationCallback property ([PublicAPI], [JsonIgnore]), next to HandlebarsRegistrationCallback.
• TransformerFactory now passes the settings to ScribanContextFactory. The factory invokes the callback with a new ScriptObject each time it creates a transformer context, the same lifetime as the Handlebars callback.
• ScribanContext builds the TemplateContext itself when custom globals exist (LiquidTemplateContext for DotLiquid), pushing the custom globals first and the model second. When no callback is configured, it still calls Template.Render(model, renamer) exactly as before, so existing users see no change.
• New WireMockServerSettingsExtensions.WithScribanRegistration(Action<ScriptObject, IFileSystemHandler>) in WireMock.Net.Minimal gives a strongly typed alternative. It keeps any callback that is already configured and runs it first, so several libraries can register functions.
• The .NET 8 console example shows a greet function used from a Scriban mapping.

Tests

• ScribanContextFactoryTests: callback invoked once per context with a ScriptObject and the settings' IFileSystemHandler, and a new ScriptObject per context.
• ScribanContextTests (new): custom functions with and without arguments (Liquid as a filter), model precedence over custom globals, custom globals over Scriban built-ins, template assignments not mutating custom globals, and output parity with and without an empty set of custom globals for both Scriban types.
• ResponseWithScribanTests: the custom function in the body, a header and a JSON body, for both Scriban types.
• WireMockServerSettingsTests: an HTTP round trip against a running server, for both Scriban types.
• WireMockServerSettingsExtensionsTests (new): typed callback, chaining order and argument guards.

Test reliability fixes

These tests failed in environments without outbound internet or IPv6, independent of this feature:

• WireMockServerProxyTests: seven tests proxied to http://www.google.com. They now proxy to a local WireMockServer started per test, so they no longer depend on the network. Two of them (..._Should_Not_SaveMapping) and WireMockServer_Proxy_Should_proxy_responses previously passed even when the proxy call failed; they now exercise a real proxied response, and the latter asserts the exact proxied body.
• WireMockServer_Should_respond_to_ipv6_loopback is skipped at runtime with Assert.SkipUnless(Socket.OSSupportsIPv6, ...) when the OS has no IPv6 support, instead of failing with a socket error.