feat(core-testing): RecordingEventBus

Adds RecordingEventBus implementing IEventBus for use in unit tests.
Validates payloads via the descriptor schema, records all publish calls,
and delivers events to subscribed handlers synchronously in subscription order.

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

packages/core-testing/package.json

@@ -21,8 +21,10 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "@repo/core-events": "workspace:*",
     "@repo/core-shared": "workspace:*",
     "@testing-library/jest-dom": "^6.5.0",
+    "zod": "^3.23.0",
     "@testing-library/react": "^16.0.0",
     "@testing-library/user-event": "^14.5.0",
     "@trpc/client": "^11.0.0",