feat(perf): Optimize feed tag extraction with caching

- Extracted `getVideoTags` to `js/feedEngine/utils.js` with `WeakMap` caching.
- Updated `js/feedEngine/stages.js` and `js/feedEngine/kidsScoring.js` to use the cached utility.
- Removed redundant `collectVideoTags` and `normalizeTagSetFromVideo` functions.
- Added `benchmarks/feed_tags.mjs` to measure performance (approx 25x speedup in tight loops).
- Updated `hasDisinterestedTag` in `utils.js` to use the new utility.

This reduces object allocation and repeated string normalization during feed processing.

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

js/feedEngine/utils.js

@@ -4,6 +4,8 @@ import { normalizeHashtag } from "../utils/hashtagNormalization.js";
 
 export const NORMALIZED_ARRAY_MARKER = Symbol("FeedItemsNormalized");
 
+const videoTagCache = new WeakMap();
+
 export function markAsNormalized(items) {
   if (Array.isArray(items)) {
     items[NORMALIZED_ARRAY_MARKER] = true;
@@ -39,33 +41,54 @@ export function toArray(value) {
   return [value];
 }
 
+export function getVideoTags(video) {
+  if (!video || typeof video !== "object") {
+    return new Set();
+  }
+
+  if (videoTagCache.has(video)) {
+    return videoTagCache.get(video);
+  }
+
+  const normalized = new Set();
+
+  const addTag = (rawTag) => {
+    if (typeof rawTag !== "string") {
+      return;
+    }
+    const tag = normalizeHashtag(rawTag);
+    if (tag) {
+      normalized.add(tag);
+    }
+  };
+
+  if (Array.isArray(video.tags)) {
+    for (const tag of video.tags) {
+      if (Array.isArray(tag) && tag[0] === "t" && typeof tag[1] === "string") {
+        addTag(tag[1]);
+      }
+    }
+  }
+
+  if (Array.isArray(video.nip71?.hashtags)) {
+    for (const tag of video.nip71.hashtags) {
+      addTag(tag);
+    }
+  }
+
+  videoTagCache.set(video, normalized);
+  return normalized;
+}
+
 export function hasDisinterestedTag(video, disinterestsSet) {
   if (!video || !disinterestsSet || !(disinterestsSet instanceof Set) || disinterestsSet.size === 0) {
     return false;
   }
 
-  const matchesDisinterest = (tag) => {
-    const normalized = normalizeHashtag(tag);
-    return Boolean(normalized && disinterestsSet.has(normalized));
-  };
-
-  // Check raw tags
-  if (Array.isArray(video.tags)) {
-    for (const tag of video.tags) {
-      if (Array.isArray(tag) && tag[0] === "t" && typeof tag[1] === "string") {
-        if (matchesDisinterest(tag[1])) {
-          return true;
-        }
-      }
-    }
-  }
-
-  // Check NIP-71 metadata hashtags if available
-  if (video.nip71 && Array.isArray(video.nip71.hashtags)) {
-    for (const tag of video.nip71.hashtags) {
-      if (typeof tag === "string" && matchesDisinterest(tag)) {
-        return true;
-      }
+  const tags = getVideoTags(video);
+  for (const tag of tags) {
+    if (disinterestsSet.has(tag)) {
+      return true;
     }
   }