Add test that verifies embeddings aren't supported

xAI currently returns no embedding models, which is the reason we don't provide an IEmbeddingGenerator implementation. If this changes in the future, this new test will fail and we can fix that by providing an implementation then.

Author: kzu

src/xAI.Protocol/Extensions.cs

@@ -19,7 +19,7 @@ public async Task<IEnumerable<LanguageModel>> ListLanguageModelsAsync(Cancellati
         }
 
         /// <summary>Lists available embedding models.</summary>
-        public async Task<IEnumerable<EmbeddingModel>> ListEmbeddingModelsAsync(CancellationToken cancellation)
+        public async Task<IEnumerable<EmbeddingModel>> ListEmbeddingModelsAsync(CancellationToken cancellation = default)
         {
             var models = await client.ListEmbeddingModelsAsync(new Empty(), cancellationToken: cancellation);
             return models.Models;

src/xAI.Tests/SanityChecks.cs

@@ -10,6 +10,21 @@ namespace xAI.Tests;
 
 public class SanityChecks(ITestOutputHelper output)
 {
+    [SecretsFact("CI_XAI_API_KEY")]
+    public async Task NoEmbeddingModels()
+    {
+        var services = new ServiceCollection()
+            .AddxAIProtocol(Environment.GetEnvironmentVariable("CI_XAI_API_KEY")!)
+            .BuildServiceProvider();
+
+        var client = services.GetRequiredService<Models.ModelsClient>();
+
+        var embeddings = await client.ListEmbeddingModelsAsync();
+
+        Assert.NotNull(embeddings);
+        Assert.Empty(embeddings);
+    }
+
     [SecretsFact("CI_XAI_API_KEY")]
     public async Task ListModelsAsync()
     {