Fix flaky cancelAsyncOperationAbandon test signal pollution

The ABANDON cancel-before-sent sub-test can start a handler workflow that
sets the shared opStarted/handlerFinished signals, causing the subsequent
after-start sub-test to proceed with stale signal state and fail. Clear
both signals between the two sub-tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bergundy

temporal-sdk/src/test/java/io/temporal/workflow/nexus/CancelWorkflowAsyncOperationTest.java

@@ -135,6 +135,11 @@ public void cancelAsyncOperationAbandon() {
     // Cancel before command is sent
     runCancelBeforeSentTest(NexusOperationCancellationType.ABANDON);
 
+    // For ABANDON, the handler workflow may start even in the cancel-before-sent case,
+    // which can set opStarted and handlerFinished. Clear them before the after-start test.
+    opStarted.clearSignal();
+    handlerFinished.clearSignal();
+
     // Cancel after operation is started
     WorkflowStub stub =
         testWorkflowRule.newUntypedWorkflowStubTimeoutOptions("TestNexusOperationCancellationType");