BuildNotes v1.2.3-1.21.9

Fix: Prevent Server Scope data leaking into other worlds

Corrects a memory leak where Server Scope notes and builds persisted in the client's static cache (ClientCache) after disconnecting from a dedicated server.

The issue occurred because the cache clearing logic was wrapped in `client.execute()`, which placed the cleanup task on the end of the Main Thread queue. When a user quickly disconnected and then loaded a Singleplayer world or joined a second server, the cache clearing was often delayed or discarded, allowing the old data to bleed into the new session.

The fix involves running `ClientCache.clear()` and `ClientSession.leaveServer()` synchronously on the Netty network thread during the `ClientPlayConnectionEvents.DISCONNECT` event, guaranteeing immediate memory cleanup.

# Conflicts:
#	gradle.properties