`panic` does not trigger a failed test when within a JavaScript Promise

I was experimenting with tests involving large amounts of JS Promises, and noticed that gleeunit ran into some issues with code involving Promises.

Here is a minimal example that passes in gleeunit but fails when run directly:

```gleam
import gleam/javascript/promise
import gleeunit

pub fn main() -> Nil {
gleeunit.main()
}

pub fn main_test() -> Nil {
echo "testing"
let promise1 =
promise.new(fn(resolve) {
echo "testing promise"
panic
resolve("Hello, World!")
})

Nil
}
```

The expected behavior is to match Node/Deno/Bun, which all throw errors in execution.

Start by running the minimal Gleam example through gleeunit.main and compare its behavior with direct execution under Node, Deno, and Bun. Trace how gleeunit handles Promise callbacks and panic failures; done means the example reports a failed test rather than passing, consistently with those runtimes.

Written by the indexing model from the issue text.