Record cache reuse probes and reset each benchmark configuration

perf/baseline.mjs

@@ -761,6 +761,9 @@ async function main() {
       results.browsers[bName] = {};
 
       for (const prof of profiles) {
+        // The preceding profile can end on a synthetic feature-update tree.
+        // Always measure the actual base build on the next cold visit.
+        await server.restartWithPublic(treeBase);
         console.log(`\n>>> Running Benchmark: Browser=[${bName}] Profile=[${prof}]`);
         results.browsers[bName][prof] = {};