Fix singleplayer disconnect on ESC pause: freeze dimension loops

- New client mixin MixinMinecraftPauseDetector: on each Minecraft.runTick, detect integrated-server pause and freeze/unfreeze all dimension loops via DimThreadCore.setPaused, so no worker writes LevelChunk while the main thread is saving/pausing. Fixes reproducible disconnect (packet decode IndexOutOfBounds on ClientboundLevelChunkWithLight) ~0.5s after opening the pause menu.

- LevelTickLoop: add pause()/resume() (cancel next tick, stop self-rescheduling, re-schedule on resume) plus a paused guard at run() entry. Resilient to RejectedExecutionException when the master pool is already shut down.

- ServerManager.setPaused: pause all loops, then wait up to 5s for the in-flight tick to fully settle before returning.

- Keep existing work: TE whitelist command (/dimensionalripper tewhitelist), shard drop counters (entity/TE/chunk-env), POI lock optimization.

src/main/resources/dimensionalripper.mixins.json

@@ -64,6 +64,7 @@
         "YieldJobSiteGuardMixin"
     ],
     "client": [
+        "MixinMinecraftPauseDetector"
     ],
     "server": [
     ],