uv python uninstall error message for invalid requests is confusing

[zanieb]

e.g.

❯ cargo run -q -- python uninstall any
warning: `uv python uninstall` is experimental and may change without warning.
error: Cannot download managed Python for request: executable name `any`

We should wrap this error to be clearer, i.e. we're not trying to download here but instead trying to suggest the request can't be mapped to a managed Python key.

[charliermarsh]

Relatedly, do you want a way to uninstall all Pythons?

[zanieb]

Yeah we should probably support that, though I think it should require some sort of opt-in.

[charliermarsh]

I could either see... python uninstall all or python uninstall --all (mutually exclusive with a request).