Run multi-user scenarios in a single Playwright test using parallel browser contexts

Steps

1. Call browser.newContext() twice inside one test to create two isolated contexts, each with its own cookies, localStorage, and session state
2. Open a page in each context and authenticate each as a different user, storing credentials only within that context
3. Perform actions in both pages — for example, user A sends a message and user B receives it — asserting against both pages in the same test
4. Close both contexts explicitly at the end of the test to release resources; Playwright does not auto-close manually created contexts
5. For worker-level reuse, create shared contexts in a fixture with scope: 'worker' so the same authenticated pair is shared across tests in a worker