Rip out the extensible/user serialisation system.•••This was part of a failed attempt to implement zero downtime
restarts in v3. This can be implemented in a better way but for
now its just slowing down build times so lets kill it.
Move aptosa/untosa into the sockaddrs union and add from/from_ip.•••The struct will also now always be zero-initialized by default which
removes the footgun which has happened previously where the union has
been accessed before being initialized leading to it containing weird
values.