Binary packed network addresses

Consider url network addresses like:

```
tcp4://127.0.0.1:1234
udp4://10.20.30.40:5060
ws://1.2.3.4:5678
tcp6://[1fff:0:a88:85a3::ac1f]:8001
```

How best to binary pack them? Is there a standard for this? These should be storable in 7 bytes for IPv4 (not 20), and 19 bytes for ipv6 (not 35).

If not, perhaps:

```
<1 byte proto><4 or 16 byte ip><2 byte port>
```

Or, if we want encapsulation generality:

```
(<1 byte proto>)+
<1 byte ipv4 code><4 byte ipv4 addr><1 byte udp code><2 byte udp port>
<1 byte ipv6 code><16 byte ipv6 addr><1 byte tcp code><2 byte tcp port>
```

Which is nice, because it stacks well.

Back-translating with a better hierarchical approach (let's not get too crazy now...) gives us:

```
(//)+
/ip4//udp/
/ip6//tcp/
```

Rather than:

```
udp4://:
tcp6://[]:
```

No files, tests, or implementation entry points are identified. Start by comparing the example network addresses with the proposed fixed-width and hierarchical encodings, then check whether an existing standard is intended. Done would require an agreed binary representation and a defined back-translation format.

Written by the indexing model from the issue text.