Further optimizations to test resources

[hubertp]

Pull Request Description

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:

After:

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.

[Akirathan]

The number of alive threads dropped almost twice. Nice. Have you also, by any chance, checked the total time it takes to run language-server/test? I don't expect any drastic slowdown, just out of curiosity.

[hubertp]

Have you also, by any chance, checked the total time it takes to run language-server/test? I don't expect any drastic slowdown, just out of curiosity.

Within the same ballpark. I was experimenting with the number of threads in threadpools.