The public suffix lallows to split a fully qualified domain name
into {subdomain, domain, suffix}.

Without this file, the build process requires a download step, which is
explicitly discouraged by crates.io.

The make update new target allows to refresh the list when needed.

Improve security & reliability and avoid to introduce a supply-chain risk
and a single point of failure by fetching the list from publicsuffix.org
at build time.