Troubleshoot unresponsive GKE TPU and GPU nodes (`NodeStatusUnknown`)

When the Compute Engine host of a TPU or GPU node has a fatal hardware error, kernel panic, or non-maskable interrupt (NMI) lockup, the guest OS stops responding. The kubelet can no longer send heartbeats, so the node Ready condition becomes Unknown with Reason: NodeStatusUnknown (Kubelet stopped posting node status.). If node auto-repair is disabled on the node pool, GKE doesn't repair the node. The node can stay NotReady, and pods on it can stay in Terminating, which blocks multi-host JobSet workloads from recovering.