hint-only installers

It would be nice to have:

* `--installer=cargo`(-install?)
* `--installer=cargo-binstall`

Which produce installer hints without any need for any physical artifact. This requires some way to tell the reader of the dist-manifest that no such artifact exists, only the hint/description.

Start by tracing the installer options and dist-manifest handling mentioned in the issue. Define done as supporting cargo and cargo-binstall installer hints while clearly representing that no physical artifact exists, then verify both cases through the project's existing release or manifest checks.

Written by the indexing model from the issue text.