Whowas results are a list of all known RPL_WHOWASUSER replies.
Return the most recent event as the top level and add the
rest to a `historical` field as an array.

Example:

```
:inspircd.server.example 314 val someone ident3 127.0.0.1 * :Realname
:inspircd.server.example 312 val someone My.Little.Server :Sun Mar 20 2022 10:59:26
:inspircd.server.example 314 val someone ident2 127.0.0.1 * :Realname
:inspircd.server.example 312 val someone My.Little.Server :Sun Mar 20 2022 10:59:16
:inspircd.server.example 314 val someone ident1 127.0.0.1 * :Realname
:inspircd.server.example 312 val someone My.Little.Server :Sun Mar 19 2022 9:23:06
:inspircd.server.example 369 val someone :End of WHOWAS

whowas {
  nick: 'someone',
  ident: 'ident3',
  hostname: '127.0.0.1',
  real_name: 'Realname',
  server: 'My.Little.Server',
  server_info: 'Sun Mar 20 2022 10:59:26',
  historical: [
    {
      nick: 'someone',
      ident: 'ident2',
      hostname: '127.0.0.1',
      real_name: 'Realname',
      server: 'My.Little.Server',
      server_info: 'Sun Mar 20 2022 10:59:16'
    },
    {
      nick: 'someone',
      ident: 'ident1',
      hostname: '127.0.0.1',
      real_name: 'Realname',
      server: 'My.Little.Server',
      server_info: 'Sun Mar 19 2022 9:23:06'
    }
  ]
}
```

Fixes: kiwiirc#371

Return all results in event.historical