internal/core/eval: add testcase for https://github.com/cue-lang/cue/issues/2566 issue

[bozaro]

Based on PR:

• cue/stats: add metric for builtin calls #2587

[mvdan]

Thanks for these PRs! You might want to use Gerrit instead of GitHub for your contributions, because that's the source of truth for git and where we do the vast majority of our code reviews, and on top of that you can "chain" your CLs (commits) via a branch. That ends up being a lot nicer to review and merge than with GitHub PRs, where you have to either keep one PR with many commits, or awkwardly "stack" your PRs on top of one another by accumulating commits.

For example, see this stack of CLs by Roger which we reviewed and merged recently: https://review.gerrithub.io/c/cue-lang/cue/+/1170886

https://github.com/cue-lang/cue/blob/master/CONTRIBUTING.md should have more info.