[Bug] W&B initialization fails with wandb 0.28.2 because wandb.util.generate_id was removed

Bug Description

On the latest Slime main branch, init_wandb_primary() calls wandb.util.generate_id() when wandb_random_suffix is enabled.

wandb.util.generate_id() is no longer available in W&B 0.28.2, so W&B initialization fails with an AttributeError before training starts. The same code path works with W&B 0.28.1, where the legacy wrapper still exists.

Steps to Reproduce

1. Check out Slime main at commit a3f5009 or a version containing the same call in slime/observability/wandb_utils.py.
2. Install wandb==0.28.2.
3. Run the following minimal reproduction:

from types import SimpleNamespace

from slime.observability.wandb_utils import init_wandb_primary

args = SimpleNamespace(
    use_wandb=True,
    wandb_mode="offline",
    wandb_key=None,
    wandb_host=None,
    wandb_random_suffix=True,
    wandb_group="wandb-repro",
    rank=0,
)

init_wandb_primary(args)

Expected Behavior

Slime should generate the random W&B group suffix and continue initializing the run.

Actual Behavior

W&B initialization fails before wandb.init() is called:

Traceback (most recent call last):
  File ".../slime/observability/wandb_utils.py", line 45, in init_wandb_primary
    group = args.wandb_group + "_" + wandb.util.generate_id()
                                      ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: module 'wandb.util' has no attribute 'generate_id'

### Environment

- Slime version: `main` at `a3f5009`
- Python version: 3.12.3
- W&B version: 0.28.2
- PyTorch version: not relevant; the failure occurs before training starts
- CUDA/ROCm version: not relevant
- GPU type and count: not relevant
- OS: Ubuntu 24.04
- SGLang version: not relevant
- Megatron-LM version: not relevant

### Logs

```shell

Additional Context

W&B 0.28.1 still provides wandb.util.generate_id() as a legacy wrapper, but W&B 0.28.2 removes it. The run-ID generator remains available from wandb.sdk.lib.runid in W&B 0.28.2.

One possible fix is:

from wandb.sdk.lib.runid import generate_id

group = args.wandb_group + "_" + generate_id()

I verified this replacement with both wandb==0.28.1 and wandb==0.28.2 using an offline unit test.

Pre-submission Checklist

• I have read the CONTRIBUTING.md and understand the collaboration scope.
• I have read the documentation and my issue is not addressed there.
• I have searched for existing issues and this is not a duplicate.
• I have provided a minimal, reproducible example.

Start in slime/observability/wandb_utils.py at init_wandb_primary() and reproduce the failure with wandb==0.28.2 using the offline example from the issue. Verify that W&B initialization succeeds with wandb_random_suffix enabled under both wandb==0.28.1 and 0.28.2, using the offline unit test mentioned in the report.