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]

[alloc object]

### Anything else we need to know?

_No response_