perf: implement IndexedDB connection pooling and fix channel profile regression

- Implemented IndexedDB connection pooling in `js/storage/dmDb.js` to reduce connection overhead.
- Removed `async` from `collectChannelVideos` in `js/channelProfile.js` to fix `TypeError: matches is not iterable` in unit tests.
- Added benchmark script for DM database operations.

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

js/channelProfile.js

@@ -238,7 +238,7 @@ function decorateChannelVideo(video, app = getApp()) {
   return decoratedVideo;
 }
 
-export async function collectChannelVideos(pubkey, app = getApp()) {
+export function collectChannelVideos(pubkey, app = getApp()) {
   const normalized = normalizeHex(pubkey);
   if (!normalized) {
     return [];