Brainstorm: something to check package name doesn't clash with PyPI

[nathanjmcdougall]

Motivation
When creating a project with uv init, we might create a project which can't be uploaded to PyPI because it's name is wrong. Some thinking required about how to solve this. It might really be a uv feature request - although usethis might (likely?) end up with its own init strategy in the long run. It might just be a convenience function to check if the name is free or not. But in any case some strategy needed.

Summary of desired enhancement
Brainstorm a way to check whether a package name is used on PyPI and possibly a way to prevent it during init.