bug: The VLLMRuntime controller fails on every reconciliation when running on a cluster that does not have KEDA installed

Describe the bug

The VLLMRuntime controller fails on every reconciliation when running on a cluster that does not have KEDA installed, even if no VLLMRuntime resource enables autoscaling. This makes the operator unusable on clusters without KEDA.

To Reproduce

Environment

• vLLM Production Stack Operator
• Cluster without KEDA (no keda.sh API group registered)

Steps to Reproduce

1. Install the operator on a cluster without KEDA
2. Create a VLLMRuntime resource without autoscalingConfig (or with autoscalingConfig.enabled: false)
3. Observe the controller logs

Expected behavior

The VLLMRuntime reconciles successfully. Since autoscaling is not requested, the operator should not require KEDA to be present.

Additional context

Root cause:

In operator/internal/controller/vllmruntime_controller.go:360-370, when autoscalingConfig is nil or disabled, the else branch attempts to delete a ScaledObject as a cleanup measure:

https://github.com/vllm-project/production-stack/blob/9b78da7dd9df3652bea4cddaa31d9087497cebc8/operator/internal/controller/vllmruntime_controller.go#L360-L370

The guard !errors.IsNotFound(err) only catches the case where the ScaledObject resource does not exist (i.e., the keda.sh API group is registered, but no ScaledObject with that name is found). It does not catch the case where the keda.sh API group itself is not registered on the cluster. In that scenario, the API server returns a different error (e.g., "the server could not find the requested resource") that does not satisfy errors.IsNotFound(), causing the reconciliation to fail.

Start in operator/internal/controller/vllmruntime_controller.go around lines 360-370 and reproduce the reconciliation on a cluster without the keda.sh API group, using a VLLMRuntime with autoscaling omitted or disabled. Confirm the controller behavior for that scenario and verify that reconciliation succeeds without KEDA while autoscaling remains unrequested.