tests: add test for cache control type static class

tests/AnthropicClient.Tests/Unit/Models/CacheControlTypeTests.cs

@@ -0,0 +1,10 @@
+namespace AnthropicClient.Tests.Unit.Models;
+
+public class CacheControlTypeTests
+{
+  [Fact]
+  public void Ephemeral_WhenCalled_ItShouldReturnExpectedValue()
+  {
+    CacheControlType.Ephemeral.Should().Be("ephemeral");
+  }
+}