## Summary

This PR updates the vitest test runner integration to use the modern
`--no-file-parallelism` flag instead of the deprecated
`--poolOptions.forks.minForks=0` and `--poolOptions.forks.maxForks=1`
flags.

## Changes

- Replaced verbose pool options with `--no-file-parallelism` flag in
both file-level and symbol-level vitest test tasks
- This change works with vitest v4 while maintaining backwards
compatibility with earlier versions (or 3 at least!)

## Testing

- Added test `test_vitest_uses_no_file_parallelism_flag` that verifies:
  - The `--no-file-parallelism` flag is present in generated test tasks
  - The deprecated `poolOptions` flags are not present
- Manually tested with both vitest v4 and older versions to confirm
backwards compatibility
- All existing tests pass

## Impact

This allows Zed users to run and debug vitest tests in projects using
vitest v4 while maintaining support for earlier versions.

Release Notes:

- Fixed vitest test running and debugging for projects using vitest v4

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Co-authored-by: Cole Miller <cole@zed.dev>