`ethexe`: setup validators in fast-sync (maybe)

```
    // TODO: whether we need to setup validators here?
```

In file ethexe/service/src/fast_sync.rs
https://github.com/gear-tech/gear/blob/d6a2523d857ec78a319a9b590ba080660b2c9f44/ethexe/service/src/fast_sync.rs#L731