Rework withKVDB

The function currently is just an alias for `evalKVDB`:

```haskell
evalKVDB :: forall db a. D.DB db => D.DBHandle db -> L.KVDBL db a -> LangL a

withKVDB :: forall db a. D.DB db => D.DBHandle db -> L.KVDBL db a -> LangL a
withKVDB = evalKVDB
```

But it can be more high level:
```haskell
withKVDB :: forall db a. D.DB db => D.KVDBConfig db -> L.LangL a -> LangL a
```