Turbopack: Fix some eventually consistent reads at the top level in dev-server and snapshot tests (#90792)
This fixes
```
UPDATE=1 cargo test -p turbopack-tests
```
when a snapshot test output is modified or deleted.
We must get the `Effects` inside of an operation, as that involves reading `Vc`s, but then we should apply them outside of the operation (to guarantee that they only run once). The Next.js code follows a similar pattern here.