Publish artemis-client to PyPI

Hi! I’d like to use Artemis as a Python library in another project.

At the moment, the client has to be installed directly from GitHub:

```bash
uv add "artemis-client @ git+https://github.com/google/artemis.git#subdirectory=packages/artemis-client"
```

Would you consider publishing `packages/artemis-client` to PyPI?

That would make installation and dependency management much simpler:

```bash
uv add artemis-client
# or
pip install artemis-client
```

It would also make it easier to pin SDK versions and use Artemis in reproducible project environments.

Is a PyPI release planned? I’d be happy to help test it or contribute if useful.

Start by inspecting packages/artemis-client and the repository's existing Python package metadata and release configuration. Verify the package can be built and installed independently, then test the publishing path and confirm that `pip install artemis-client` or `uv add artemis-client` works with a reproducible version.

Written by the indexing model from the issue text.