Before making changes, move router pick address functions to their own C file
As part of Sponsor 55, let's move these relay functions to their own C files:
In src/feature/relay/resolve_addr_relay.c
- router_pick_published_address()
In src/app/config/resolve_addr.c
- resolve_my_address()
- get_last_resolved_addr()
- reset_last_resolved_addr()
- last_resolved_addr
- is_local_addr()
- is_local_addr_impl()
These are relay-level now, but I think they should become client-level:
- router_new_address_suggestion()
- router_guess_address_from_dir_headers()
We should also move any related functions.
And write unit tests :-)