Updates `NostrClient.subscribeVideos` to buffer incoming events and invoke the `onVideo` callback once per flush cycle with an array of updates, instead of once per video. This significantly reduces redundant sorting, filtering, and persistence operations in `NostrService`.
Also optimizes `populateNip71MetadataForVideos` to run as a single batched request per flush cycle.
BREAKING CHANGE: `subscribeVideos` callback now receives `Video[]` instead of `Video`. All internal consumers have been updated.
Co-authored-by: PR0M3TH3AN <[email protected]>