fix: guard onPlayerUpdate against non-Player entities

[Bobbyperson]

DAGeneralEvents.onPlayerUpdate is subscribed to EntityTickEvent.Post, which fires for every ticking entity, but it casts the entity to Player after only an attachment check. Any non-player entity carrying DAAttachments.PLAYER reaches the cast and throws ClassCastException, crashing the server.

On a 1.21.1 / NeoForge 21.1.231 dedicated server this showed up as a crash loop. The real exception was masked by ServerHangWatchdog reports (a single server tick took 60000004.00 seconds), the actual cause was only in latest.log:

ClassCastException: Villager cannot be cast to Player
  at DAGeneralEvents.onPlayerUpdate(DAGeneralEvents.java:261)
  via fireEntityTickPost -> Ticking entity -> server shutdown