For generators are eager in values, but should be lazy

```groovy
x = new {
["one"] = 1
["two"] = this["one"] + 1
}

y = (x) {
for (k, v in x) {
[k] = v + 1
}
}
```

Here, `y["two"]` should be 4, not 3.

`for (v in x) {}` should iterate over lazy values, and `for (k, v in x) {}` should iterate over eager keys and lazy values.

The issue names no file, test, or entry point. Start by locating the implementation and tests for generator for-loops, then verify the example produces y["two"] as 4 and that single-value iteration remains lazy.

Written by the indexing model from the issue text.