fix `compile::value::compile_value` return types

Currently this:

```yaml
// data = { my_string: "5" }
value: ${{ my_string }}
```

will compile to:

```yaml
value: 5
```

because we are guessing the return type in `compile::value::compile_value`, based on the value. 

With #4 we should now be able to return the correct type based on the value from data.