Add entity sharding (ShardGate) and POI lock optimization

- ShardGate: shard entity ticking into per-shard CAS gates so slow shards
  skip a tick instead of blocking the whole barrier
- EntityTickParallel: collect entities by stable id into shards, submit via
  ShardGate, count missed shards
- FineGrainScheduler: add submitShard path with gate release and barrier
  counting
- SectionStorageMixin: replace global exclusive synchronized map with
  ConcurrentLong2ObjectMap to remove the POI read lock bottleneck
  (~19k villagers: TPS 9 -> 20)
- MasterCommand: add 'fine sharded on|off' toggle and status display
- Add environment setup/launch scripts

初始化环境.bat

@@ -0,0 +1,25 @@
+@echo off
+chcp 65001 >nul
+REM 一键初始化 NeoForge 1.21.1 开发环境
+REM 会自动下载 gradle-wrapper.jar 并刷新依赖
+
+cd /d "%~dp0"
+
+echo ========================================
+echo   正在初始化 NeoForge 1.21.1 开发环境
+echo ========================================
+echo.
+
+powershell -ExecutionPolicy Bypass -File "setup.ps1"
+
+if %errorlevel% neq 0 (
+    echo.
+    echo 初始化过程中出现错误，请检查网络连接或手动下载 gradle-wrapper.jar。
+    pause
+    exit /b %errorlevel%
+)
+
+echo.
+echo 初始化完成！
+echo 你现在可以运行：gradlew runClient
+cmd /k