To not do network activity in `init` or global variables creation

seems next global variable creation:
```
var defaultClient = New()
```

Does network activity:
`NewUserConfig` -> `net.ResolveTCPAddr("tcp", fmt.Sprintf("[%s]:0", address))`
and then mutating `net.DefaultResolver.Dial `

seems it's not thread-safe in golang (in OS's C libraries which used by golang).

And on some OS this race-condition caused crash: https://github.com/erigontech/erigon/issues/12570

We still collecting evidences: i may be a bit wrong