Performance investigation for robustness test

### Which Github Action / Prow Jobs are flaking? Robustness test on ARM64 main branch ### Which tests are flaking? TestRobustnessExploratory/KubernetesHighTraffic/ClusterOfSize1/raftAfterSave=sleep ### Github Action / Prow Job link https://prow.k8s.io/view/gs/kubernetes-ci-logs/logs/ci-etcd-robustness-main-arm64/2060645815625453568 ### Reason for failure (if possible) After downloading the report and putting it under the `testdata`, I ran ``` GOFLAGS='-cpuprofile=/tmp/robustness-prof/cpu.pprof -memprofile=/tmp/robustness-prof/heap.pprof' make test-robustness-reports ``` [prof.zip](https://github.com/user-attachments/files/28427199/prof.zip) Visualization: - CPU: `go tool pprof -http=:3000 /tmp/robustness-prof/cpu.pprof` - Memory: `go tool pprof -http=:3000 -sample_index=alloc_objects /tmp/robustness-prof/heap.pprof` [CPU] <img width="1056" height="487" alt="Image" src="https://github.com/user-attachments/assets/73c755c2-40f0-4e40-be94-11bc53df4b91" /> [alloc object] <img width="1053" height="318" alt="Image" src="https://github.com/user-attachments/assets/a40de95c-c3e3-417e-85c3-2a9ac800696e" /> ### Anything else we need to know? _No response_