Add examples

[jmorrell]

Summary

• Adds worker-basic example: HTTP batch + WebSocket transport toggle with interactive playground
• Adds worker-bidirectional example: server-to-client RPC with Durable Object audit log broadcast
• Returns RpcSession from WebSocket helpers instead of a proxy, giving callers access to session.onClose() for connection lifecycle management
• Adds onClose(handler) and Symbol.dispose to RpcSession

API changes

newWorkersWebSocketRpcSession now returns { response, session } instead of { response, remote }:

const { response, session } = newWorkersWebSocketRpcSession<ClientApi, typeof service>(
  request,
  service,
);

session.remote.onEvent(event);           // call methods on the client
session.onClose(() => cleanup());        // clean up when connection drops

newWebSocketRpcSession now returns an RpcSession instead of a proxy:

const session = newWebSocketRpcSession<ServerApi>(wsUrl);
await session.remote.add(1, 2);          // was: await proxy.add(1, 2)
session.close();

Test plan

• All 163 existing tests pass
• New tests for onClose (transport close, session close, already-closed, multiple handlers)
• New test for Symbol.dispose on RpcSession
• Manual: run worker-bidirectional example, open two tabs, verify audit events broadcast, close a tab and verify subscription cleanup via onClose