We're not sure what the best way to expose the native store to users is
yet and it's a bit weird that you can use this in the `uv auth` commands
but can't use any of the other keyring provider options. The simplest
path forward is to just not expose it to users as a keyring provider,
and instead frame it as a preview alternative to the plaintext uv
credentials store. We can revisit the best way to expose configuration
before stabilization.
Note this pull request retains the _internal_ keyring provider
implementation — we can refactor it out later but I wanted to avoid a
bunch of churn here.
Zanie Blue
709e0ba238