TestRuntime should be deprecated as it creates a number of threads and doesn't allow to easily modify ZIO's runtime.
But the biggest drop stems from fixing leaking `FileSystemService` that weren't being closed for every `TextOperationsTest` test.
The change is a follow up on #8892 but this time focused on ZIO usage.

Hopefully fixes #8806 for good.

# Important Notes
Running `language-server/test`.
Before:
![Screenshot from 2024-02-02 09-48-32](https://github.com/enso-org/enso/assets/292128/fb414c74-7d7a-4e7b-8b0c-d25dc3721bbf)

After:
![Screenshot from 2024-02-02 09-46-02](https://github.com/enso-org/enso/assets/292128/db9429df-d861-4f48-818f-888d5bbbb089)