`list` command doesn't properly display packages without binaries

[chalkygames123]

Hi,

In Volta v1.0.8, the list command outputs just (default) for packages that do not have binaries as follows:

% volta install node@latest vue
success: installed and set [email protected] (with [email protected]) as default
success: installed [email protected]

% volta list                   
⚡️ Currently active tools:

    Node: v18.6.0 (default)
    Tool binaries available:
         (default)

See options for more detailed reports by running `volta list --help`.

This seems to be due to the broken plain format (notice the consecutive slashes):

% volta list --format=plain 
runtime [email protected] (default)
package [email protected] / / [email protected] npm@built-in (default)