Function open_cache 

pub fn open_cache(
    env: &impl EnvSource,
    base: Option<PathBuf>,
    bin: &Path,
    refresh: bool,
) -> IssueCache

The cache route and verify-decision fetch through.

Configured from env, rooted under base (dirs::cache_dir()), namespaced to the gh login (see auth_scope), and swept of expired entries. Blocking.