explicitly add chunk flags to evaluator calls

Allowing chunk flags would allow language plugins to push whatever metadata they want into the evaluator itself, allowing things like this:

```javascript
%% async-language returnValueName="dataset"

let data = await fetch(...)
let otherData = await fetch('https://path.to/data')

if (blahblahblah) {
// do some other async logic here
}
data // this is the final return data
```

And theoretically this would allow the language plugin evaluator to utilize that `returnValueName` flag.

This should be a pretty straightforward addition – all we need to do is pass in the flags directly into the evaluator in `src/eval-frame/actions/actions.js`, lines 65 or 82 (I think).

Start in src/eval-frame/actions/actions.js at the evaluator calls around lines 65 and 82, then trace how chunk flags are represented and passed through the language-plugin path. Done means evaluator calls receive the chunk flags so plugins can use metadata such as returnValueName; verify the existing evaluator behavior and tests if present.

Written by the indexing model from the issue text.