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

启动环境.bat

@@ -0,0 +1,24 @@
+@echo off
+REM NeoForge 1.21.1 模组开发环境启动脚本
+set JAVA_HOME=C:\Program Files\Java\jdk-21
+set PATH=%JAVA_HOME%\bin;%PATH%
+
+echo ========================================
+echo   Minecraft 1.21.1 NeoForge 开发环境
+echo ========================================
+echo.
+echo Java版本:
+java -version
+echo.
+echo Gradle任务列表:
+echo   runClient      - 启动Minecraft客户端测试
+echo   runServer      - 启动专用服务器测试
+echo   runData        - 运行数据生成器
+echo   build          - 构建模组JAR文件
+echo   idea           - 生成IntelliJ IDEA项目文件
+echo.
+echo 当前目录: %cd%
+echo.
+echo 输入 gradlew 任务名 来执行，例如: gradlew runClient
+echo.
+cmd /k