fix: guard Linux-only platform helpers

[saurabhhhcodes]

Summary

• move the CPU chaos scenario sleep call behind a platform helper
• keep Linux on unix.Nanosleep so scheduler wakeup behavior is preserved
• use time.Sleep on non-Linux platforms so the chaos package can compile and run targeted tests on macOS
• guard the Linux inotify-based audit implementation behind linux build tags
• add a non-Linux audit command stub that reports the unsupported platform instead of breaking compilation

Validation

• env GOCACHE=/private/tmp/kerno-go-build-cache go test ./internal/chaos -run 'TestScenarios/cpu|TestRunDispatchesScenario|TestRegistryHasAllScenarios|TestIntensity|TestPaired' -count=1
• env GOCACHE=/private/tmp/kerno-go-build-cache go test ./internal/chaos -run '^$'
• env GOCACHE=/private/tmp/kerno-go-build-cache GOOS=linux GOARCH=amd64 go test -c -o /private/tmp/kerno-chaos-linux.test ./internal/chaos
• env GOCACHE=/private/tmp/kerno-go-build-cache go test ./cmd/kerno -run '^$'
• env GOCACHE=/private/tmp/kerno-go-build-cache go test ./internal/cli -run 'Test.*Audit|TestRoot|TestCompletion|Test.*Flags' -count=1
• env GOCACHE=/private/tmp/kerno-go-build-cache GOOS=linux GOARCH=amd64 go test -c -o /private/tmp/kerno-linux.test ./cmd/kerno
• git diff --check

The full go test ./internal/chaos package run is still blocked in this sandbox by the unrelated tcp-churn smoke test requiring a local TCP listener: listen tcp 127.0.0.1:0: bind: operation not permitted.

[github-actions]

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