`--bind` becomes repeatable, so one process can serve several addresses:
an explicit IPv4 and IPv6 pair on one port, or two interface addresses
that must stay distinct.
The applet now builds a `ServerSet` for every invocation, including a
single bind. There is deliberately no bind-count branch and no direct
path from the CLI to `Server`: one orchestration path means startup
errors, shutdown and listener-failure handling are identical whatever was
configured, and the single-listener case — the common one — keeps that
path exercised in normal use rather than only in tests.
The configuration stays one `ServerConfig`; addresses never enter it, and
`ServerSet` clones it into each listener. Bounds in it are therefore per
listener, which `--max-sessions` help now says. Listener lines are
printed only once the whole set is up, so a set whose second bind fails
no longer announces the first as listening.
The shutdown flag, its polling future and the current-thread runtime are
unchanged: exactly one shutdown future is created and the set fans it out
internally.
Nils Andreas Svee
2171d02203