Fix test server to return INVALID_ARGUMENT for UNHANDLED_COMMAND (#2757)

The real Temporal server returns INVALID_ARGUMENT error when a workflow
task has unhandled commands. The test server was silently recording the
failure in history but returning success to the caller, causing the SDK
to apply completion metrics before learning the task was rejected.

This fix makes the test server throw INVALID_ARGUMENT: UnhandledCommand
to match real server behavior, preventing double-counted metrics.

Also adds registry.clear() in MetricsTest setUp for clean state.

Author: mfateev

temporal-sdk/src/test/java/io/temporal/client/functional/MetricsTest.java

@@ -63,6 +63,7 @@ public class MetricsTest {
 
   @Before
   public void setUp() {
+    registry.clear();
     tagsNamespaceQueue =
         replaceTags(TAGS_NAMESPACE, MetricsTag.TASK_QUEUE, testWorkflowRule.getTaskQueue());
   }

temporal-test-server/src/main/java/io/temporal/internal/testservice/TestWorkflowMutableStateImpl.java

@@ -488,14 +488,16 @@ public void completeWorkflowTask(
 
           if (unhandledCommand(request) || unhandledMessages(request)) {
             // Fail the workflow task if there are new events or messages and a command tries to
-            // complete the
-            // workflow
+            // complete the workflow. Record the failure in history, then throw an error to the
+            // caller (matching real server behavior).
             failWorkflowTaskWithAReason(
                 WorkflowTaskFailedCause.WORKFLOW_TASK_FAILED_CAUSE_UNHANDLED_COMMAND,
                 null,
                 ctx,
                 request,
                 false);
+            ctx.setExceptionIfEmpty(
+                Status.INVALID_ARGUMENT.withDescription("UnhandledCommand").asRuntimeException());
             return;
           }