SyncedAdvancements

1.21.9 Changed how the ServerPlayerManager is accessed (now being class-private), so SyncedAdvancements has to update in order to support the new abstraction.

This also marks the end of the Jar-in-Jar packaging, as the mod is basically feature-locked, so there isn't going to be much stuff added into it, so there will be new jars for each update instead of it trying to be an all-rounder like before. this will reduce the complexity of the project and will make me work faster to update the mod.

Nothing about SyncedAdvancements is fundamentally changed.

• Updated to 1.21.9 & 1.21.10

This version is reuploaded due to wrong gradle configuration that causes a crash