ci: shard windows tests and fix event listener leaks (#18670)

packages/cli/test-setup.ts

@@ -6,9 +6,13 @@
 
 import { vi, beforeEach, afterEach } from 'vitest';
 import { format } from 'node:util';
+import { coreEvents } from '@google/gemini-cli-core';
 
 global.IS_REACT_ACT_ENVIRONMENT = true;
 
+// Increase max listeners to avoid warnings in large test suites
+coreEvents.setMaxListeners(100);
+
 // Unset NO_COLOR environment variable to ensure consistent theme behavior between local and CI test runs
 if (process.env.NO_COLOR !== undefined) {
   delete process.env.NO_COLOR;
@@ -55,6 +59,8 @@ beforeEach(() => {
 afterEach(() => {
   consoleErrorSpy.mockRestore();
 
+  vi.unstubAllEnvs();
+
   if (actWarnings.length > 0) {
     const messages = actWarnings
       .map(({ message, stack }) => `${message}\n${stack}`)