[Feature Request] Add `py.typed` and type annotations to Python package

### Describe the feature request

It would be great if the project included type annotations and a `py.typed` file. Currently, running Mypy generates an error:

```
main.py:7: error: Skipping analyzing "onnxruntime": module is installed, but missing library stubs or py.typed marker [import-untyped]
main.py:7: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
```

- https://mypy.readthedocs.io/en/stable/installed_packages.html
- https://peps.python.org/pep-0561/

### Describe scenario use case

Running Mypy against a Python application that imports `onnxruntime` to ensure proper use.

Start by locating the Python package modules and packaging metadata in the onnxruntime repository, then review how the package is built and distributed. Use the reported Mypy scenario as the initial check. Done means the distribution includes a py.typed marker and its public Python interfaces provide annotations that Mypy can analyze without the missing-stubs error.

Written by the indexing model from the issue text.