…rsions

This allows us to remove the `put` function and we can now safely
add all addresses individually to the cache. With the addition of
the `ToSwarm::NewExternalAddrOfPeer` event, the safeguard of
overwriting all addresses in the peer cache was no longer useful
because any other behaviour would have to apply this as well.

As such, we needed to build this safe-guard directly _into_ `PeerAddresses`.

This also makes the added test pass. Previously, the events would
never get emitted because after calling `.put`, the addresses were
already in the cache and the `add`-function always returned `false`.