python api: added py.typed (#1078)

The python api library (dora-rs) is now missing py.typed, so mypy emits
error on import of dora.

In this PR, I just added py.typed to `apis/python/node/dora directory`.
Maturin automatically install the file to the package.

I've tested installation of this branch version like below, and I
confirmed py.typed is inside the site-packages/dora.

```shell
$ uv add --branch api_python-add_py_typed_marker "git+https://github.com/dieu-detruit/dora.git#subdirectory=apis/python/node"
```