Error: UMD and IIFE output formats are not supported for code-splitting builds.

I tried to use cy-rollup to test an application. However it fails with this error:

```
Error: UMD and IIFE output formats are not supported for code-splitting builds.
```

Currently code-splitting can't be disable in rollup: https://github.com/rollup/rollup/issues/2756

So, could cy-rollup use an alternative output format?
https://github.com/bahmutov/cy-rollup/blob/fd85ba5cf5795dfb7b67f4269eae4aa9ad8cf2c8/src/index.js#L38-L43

Start at src/index.js lines 38-43, where cy-rollup configures the Rollup output. Check how the current format interacts with code-splitting, then make the preprocessor use a compatible output format and verify that Cypress preprocessing no longer raises the reported error.

Written by the indexing model from the issue text.