deprecation warnings

[Jürgen Gmach]

When running the test suite via `tox` the following deprecations show up:

```
.tox/py311/lib/python3.11/site-packages/pkg_resources/__init__.py:2804
.tox/py311/lib/python3.11/site-packages/pkg_resources/__init__.py:2804
  /home/jugmac00/Source/canonical/lpci/.tox/py311/lib/python3.11/site-packages/pkg_resources/__init__.py:2804: DeprecationWarning: Deprecated call to `pkg_resources.declare_namespace('lazr')`.
  Implementing implicit namespace packages (as specified in PEP 420) is preferred to `pkg_resources.declare_namespace`. See https://setuptools.pypa.io/en/latest/references/keywords.html#keyword-namespace-packages
    declare_namespace(pkg)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
```

They probably arise from `lazr-restfulclient` and/or `lazr-uri` which are indirect dependencies via `launchpadlib`.

[Colin Watson (cjwatson)]

Deprecation warning or not, unfortunately there doesn't appear to be a reasonable migration path to implicit namespace packages. See https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#pkg-resources-style-namespace-packages:

  "If you are creating a new distribution within an existing namespace package that uses this method then it’s recommended to continue using this as the different methods are not cross-compatible and it’s not advisable to try to migrate an existing package."