refactor(bukkit): 优化物品设置反射操作

- 移除了 VersionHelper 的引用，改用新的字段名常量
- 重构了 setItem 方法，使用预先获取的 Method 和 Field 对象
- 新增了相关反射操作的静态字段，提高代码可读性和性能

bukkit/src/main/java/net/momirealms/craftengine/bukkit/util/ItemUtils.java

@@ -1,7 +1,6 @@
 package net.momirealms.craftengine.bukkit.util;
 
 import net.momirealms.craftengine.core.plugin.CraftEngine;
-import net.momirealms.craftengine.core.util.VersionHelper;
 import org.bukkit.Material;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.PlayerInventory;
@@ -20,19 +19,16 @@ public class ItemUtils {
 
     public static void setItem(PlayerInventory inventory, int slot, ItemStack itemStack) {
         try {
-            Object nmsInventory$getInventory = Reflections.clazz$CraftInventoryPlayer
-                    .getMethod("getInventory").invoke(inventory);
-            Object nmsInventory$items = Reflections.clazz$Inventory
-                    .getDeclaredField(VersionHelper.isMojmap() ? "items" : "i")
+            Object nmsInventory$getInventory = Reflections.method$CraftInventoryPlayer$getInventory
+                    .invoke(inventory);
+            Object nmsInventory$items = Reflections.field$Inventory$items
                     .get(nmsInventory$getInventory);
-            Object nmsItemStack = Reflections.clazz$CraftItemStack
-                    .getMethod("asNMSCopy", ItemStack.class)
+            Object nmsItemStack = Reflections.method$CraftItemStack$asNMSCopy
                     .invoke(null, itemStack);
             nmsInventory$items.getClass()
                     .getMethod("set", int.class, Object.class)
                     .invoke(nmsInventory$items, slot, nmsItemStack);
-        } catch (InvocationTargetException | IllegalAccessException |
-                 NoSuchMethodException | NoSuchFieldException e) {
+        } catch (InvocationTargetException | IllegalAccessException | NoSuchMethodException e) {
             CraftEngine.instance().logger().warn("Failed to set item", e);
         }
     }

bukkit/src/main/java/net/momirealms/craftengine/bukkit/util/Reflections.java

@@ -41,6 +41,7 @@ public class Reflections {
     }
 
     public static final Unsafe UNSAFE;
+    public static final String INVENTORY$ITEMS = VersionHelper.isMojmap() ? "items" : "i";
 
     static {
         try {
@@ -3894,4 +3895,25 @@ public class Reflections {
                     BukkitReflectionUtils.assembleMCClass("world.entity.player.PlayerInventory")
             )
     );
+    public static final Method method$CraftInventoryPlayer$getInventory = requireNonNull(
+            ReflectionUtils.getMethod(
+                clazz$CraftInventoryPlayer,
+                new String[]{ "getInventory" }
+            )
+    );
+
+    public static final Method method$CraftItemStack$asNMSCopy = requireNonNull(
+            ReflectionUtils.getStaticMethod(
+                    clazz$CraftItemStack,
+                    clazz$ItemStack,
+                    ItemStack.class
+            )
+    );
+
+    public static final Field field$Inventory$items = requireNonNull(
+            ReflectionUtils.getDeclaredField(
+                    clazz$Inventory,
+                    INVENTORY$ITEMS
+            )
+    );
 }