Reduce macro usage in turbo-tasks-testing (#8832)
## What?
Replaces the `turbo_tasks_testing::run!` macro with a `run` function
that requires an opaque registration argument generated by the
`register!` macro.
## Why?
A few reasons:
- `cargo fmt` doesn't work inside macros (with the exception of
function-like macros), so our tests weren't getting autoformatted.
- When a test fails, it was hard to know what line it failed on, because
the failure is attributed to the first line of the macro usage.
## Related Changes
- This also changes many (though not all) `.await?`s into
`.await.unwrap()`s. The reason for this is similar: it's easier to
attribute the line that causes a panic than the line that returns an
error. I left some tests alone as there were more `?`s than I felt like
changing.
- `register!()` now takes an optional list of other register functions
to call. The tests in `turbo-tasks-fetch` use this.
## Testing Instructions
```
cargo nextest run
```
