Add runtime heartbeats and client timeout diagnostics

[vijit-lark]

Summary

• Add runtime heartbeat messages while requests are in flight so clients can distinguish slow handlers from silent connections.
• Add Python client idle timeout and callback timeout diagnostics for assistant and artifact callbacks, plus deterministic cleanup of one-shot transport iterators to release WebSocket connections and sender tasks.
• Fix CLI integration test harness behavior after the CLI entrypoint started being spawned from Vitest, and keep the 0.14.1 package version bumps.

Test plan

• cd packages/runtimeuse && npm run build && npm run typecheck && npm test (146 passed)
• cd packages/runtimeuse && npm run test:integration (5 passed)
• cd packages/runtimeuse-client-python && uv run --with pytest --with pytest-asyncio pytest test -m "not e2e and not sandbox and not llm" -q (54 passed, 54 deselected)
• cd packages/runtimeuse-client-python && uv build

Not run: Python e2e, sandbox, and llm tests; these require external services/API-backed resources.

Made with Cursor

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