Item identity tracking, Angular 21, vscroll 1.8.3

What's Changed

• Angular 21 compatibility update (library, demo app, tests, and tooling) by @dhilt in #365
• Fixed item identity tracking to prevent Angular 21 warning NG0956 (track-by-identity full collection re-creation): rendering now uses stable item.uid, aligned with core identity persistence updates in vscroll
• Added/updated adapter coverage to validate uid uniqueness and stability across mutations (update, append, prepend, clip, reset, reload, remove)
• Updated core peer dependency requirement to vscroll@^1.8.3 (versions 1.8.0-1.8.2 are not supported in this release)

Full Changelog: v4.1.0...v4.2.0