whether the latest version is CRAN-archived (affects the source-tarball link)
whether this is an R-core / base package (recorded in SigDbPkgMeta, gates the core shard)
download count, used to rank packages into the popularity top/rest shards
the version marked as the package's latest (what a current/history tier splits on)
every fed-in version keyed by its version string
the SigDbBuilder's in-progress accumulator for one package: its metadata plus every version fed in