Fixes the missing Ray initialization (#3350)

# Description

Recent changes introduced a minor bug: now, Ray is not initialized when
`tuner.py` is called. This PR fixes this by adding back the removed
initialization.

Fixes #3349 

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Screenshots
<img width="1637" height="34" alt="pr_changes"
src="https://github.com/user-attachments/assets/820c55ce-9951-405a-ac7b-005dfeab877c"
/>


## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

scripts/reinforcement_learning/ray/util.py

@@ -343,7 +343,7 @@ def get_gpu_node_resources(
         or simply the resource for a single node if requested.
     """
     if not ray.is_initialized():
-        raise Exception("Ray is not initialized. Please initialize Ray before getting node resources.")
+        ray_init()
     nodes = ray.nodes()
     node_resources = []
     total_cpus = 0