Add a Python getting-started Jupyter notebook and reorganize the Python examples under examples/python/.
- examples/python/getting_started.ipynb: add notebook demonstrating the single-threaded tick loop (`spawn`/`send`/`tick`/`inbox`/`try_recv`) and the multi-threaded path via `RuntimeConfig` + `rt.run()`/`handle.shutdown()`
- examples/: relocate `hello_async.py` and `hello_single_thread.py` under `examples/python/`
- pyproject.toml: add a `dev` dependency group containing jupyter and ipykernel
- uv.lock: regenerate the lockfile for the new dev dependencies (2452 lines)
Signed-off-by: Zachery Aaron Shores-Chmielewski <zacheryasc@gmail.com>
