Add "eval_runner" to python package registry.

The eval runner is intended to be imported as a dependency eval projects. Thus, we need to add the eval runner to whatever the python version of pub.dev is.

Start by locating the eval_runner package and the repository's package or release configuration. Determine which Python package registry can provide the dependency workflow described in the issue, then verify that eval projects can import the published package and that the release setup is documented.

Written by the indexing model from the issue text.