Local process storage for Oi sessions.
Build a via tuple.
@type key() :: Oi.name() | {Oi.name(), role()}
@type role() :: nil | atom()
@type via_tuple() :: {:via, Registry, {Oi.Registry, key()}}
@spec key(Oi.name(), role()) :: key()
@spec via(Oi.name(), role()) :: via_tuple()