Converts the inline state maps in Is, PacketConsumer, LeaderElection, and
CircuitBreaker into structs with @type t specs. Enforced keys catch typos
on state updates and give dialyzer a concrete type to check against
instead of map() in every handle_* clause.
Is' nested login_params and packet_stats are extracted to their own
modules (Aprsme.Is.LoginParams, Aprsme.Is.PacketStats) rather than
defined inline, per the project's no-nested-modules rule.
Graham McIntire
5ef97adaf7