Optimize object allocation in kids scoring loop

- Replaced array allocation and loop with unrolled scalar comparisons in `kidsScorerStage`.
- Added unit tests and benchmark.
- Measured ~12% performance improvement (282ms -> 249ms for 200k items).

Co-authored-by: PR0M3TH3AN <[email protected]>

benchmarks/kids_scoring_bench.js

@@ -0,0 +1,63 @@
+// benchmarks/kids_scoring_bench.js
+import { createKidsScorerStage } from "../js/feedEngine/kidsScoring.js";
+import { performance } from "perf_hooks";
+
+async function runBenchmark() {
+  const itemCount = 200000;
+  const items = [];
+
+  // Create mock items with diverse data to exercise different paths
+  for (let i = 0; i < itemCount; i++) {
+    items.push({
+      video: {
+        id: `v${i}`,
+        pubkey: `pubkey${i % 100}`,
+        duration: 300 + (i % 600), // 5 to 15 minutes
+        tags: [
+          ["t", "kids"],
+          ["t", "learning"],
+          ["t", i % 2 === 0 ? "preschool" : "science"],
+        ],
+        viewCount: i * 10,
+        created_at: Date.now() / 1000 - (i % 10000),
+        moderation: { trustedCount: i % 5 },
+      },
+      metadata: {},
+    });
+  }
+
+  const context = {
+    runtime: {
+      ageGroup: "preschool",
+      trustedAuthors: ["pubkey1", "pubkey2"],
+    },
+    addWhy: () => {}, // Mock addWhy
+  };
+
+  const scorer = createKidsScorerStage();
+
+  console.log(`Starting kids scoring benchmark with ${itemCount} items...`);
+
+  // Warmup
+  await scorer([...items.slice(0, 1000)], context);
+
+  const iterations = 100;
+  let totalTime = 0;
+
+  for (let i = 0; i < iterations; i++) {
+    // Reset metadata for each run to be cleaner
+    items.forEach(item => item.metadata = {});
+
+    const start = performance.now();
+    await scorer(items, context);
+    const end = performance.now();
+    totalTime += (end - start);
+
+    if (i % 5 === 0) process.stdout.write(".");
+  }
+
+  const avgTime = totalTime / iterations;
+  console.log(`\nAverage time per run: ${avgTime.toFixed(4)}ms`);
+}
+
+runBenchmark().catch(console.error);