feat(events,session): add React-friendly subscribe APIs and snapshot getters

Adds backwards-compatible primitives needed to consume the renderer from
React 19 hooks (useSyncExternalStore, use(), TanStack Query) without
re-architecting the event bus.

- EventDispatcher.subscribe(type, cb): () => void — unsubscriber-returning
  wrapper matching the useSyncExternalStore subscribe signature.
- CommunicationManager.subscribeMessage(eventCtor, handler): () => void —
  packet-stream equivalent.
- SessionDataManager.getUserDataSnapshot() and
  RoomSessionManager.getActiveRoomSessionSnapshot() — referentially-stable
  read-only views invalidated through new SESSION_DATA_UPDATED and
  ROOM_SESSION_UPDATED events.

All additive; existing addEventListener/removeEventListener / IRoomSession
APIs are unchanged. Bumps renderer to 2.1.0.

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@nitrots/nitro-renderer",
   "description": "Javascript library for rendering Nitro in the browser using PixiJS",
-  "version": "2.0.0",
+  "version": "2.1.0",
   "private": true,
   "type": "module",
   "workspaces": [