Allow in-place pod resize to clear pod limits

[abishekgiri]

/kind bug

Summary

In-place pod resize could add or change pod-level CPU and memory limits, but it could not remove them.

If the desired pod-level limit was unset, kubelet fell back to the current cgroup value, so the old limit stayed in place. The actuated pod-level resource state could also keep the old limit when the updated pod spec no longer had that key.

This keeps a real "clear the limit" path through pod resize, uses the expected no-limit form when talking to cgroups and CRI, and updates the actuated pod-level state when a limit is removed.

Testing

• go test ./pkg/kubelet/kuberuntime -run 'TestConvertResourceConfigToLinuxContainerResources|TestDoPodResizeAction|TestValidatePodResizeAction'
• GOOS=linux GOARCH=amd64 go test -c -o /tmp/kuberuntime-linux.test ./pkg/kubelet/kuberuntime

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Details

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: abishekgiri
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[abishekgiri]

This fixes kubelet's in-place pod resize path so pod-level CPU and memory limits can actually be removed.

What changed:

• unset desired pod-level limits are no longer defaulted back to the current cgroup values
• pod cgroup writes now use the no-limit sentinel while runtime updates keep CRI's no-limit form
• memory resize validation now treats an unlimited current pod limit as an unlimited baseline
• the actuated pod-level resource record is updated even when the new pod spec omits the limit key
• tests now cover clearing pod-level CPU and memory limits

Result:

• removing a pod-level CPU or memory limit no longer leaves the old limit stuck in place
• kubelet's actuated pod-level state stays in sync with the updated pod spec after a limit is cleared

Verification:

• go test ./pkg/kubelet/kuberuntime -run 'TestConvertResourceConfigToLinuxContainerResources|TestDoPodResizeAction|TestValidatePodResizeAction'
• GOOS=linux GOARCH=amd64 go test -c -o /tmp/kuberuntime-linux.test ./pkg/kubelet/kuberuntime