Start & stop Frida between every Node test

This solves some issues where it can become totally unresponsive -
ensuring that subsequent tests recover, and that it's cleaned up so that
CI retries work successfully.

Note that the browser tests still use a single Frida process throughout.

Author: pimterry

test/frida-test-setup.ts

@@ -3,8 +3,8 @@ import { delay, isNode } from './test-util';
 if (isNode) {
     const { startFridaServer, stopFridaServer } = require("./run-frida-server") as typeof import('./run-frida-server');
 
-    before(() => startFridaServer());
-    after(() => stopFridaServer());
+    beforeEach(() => startFridaServer());
+    afterEach(() => stopFridaServer());
 } else {
     before(async () => {
         // Wait just a moment to give Frida (started via package.json script) time to start up.