Expression attribute formatting is a bit funky

When using the new channel attributes, I'm seeing formatting like the following:

```
let (looooooooooong_name0,looooooooooong_name1) = #[....]
chan<...>();
```

and think this would be better:
```
let (looooooooooong_name0,looooooooooong_name1) =
#[....]
chan<...>();
```