feat: 新增载具可堆叠规则（矿车/船堆叠至64）

mixin ItemInstance.getMaxStackSize，规则开启时矿车/船返回64，实现自动堆叠。新增item mixin分组。

src/main/java/com/github/zly2006/carpetslsaddition/SLSCarpetSettings.java

@@ -77,4 +77,7 @@ public class SLSCarpetSettings {
 
     @Rule(categories = {SLSA, RuleCategory.FEATURE})
     public static boolean unbreakableDecoratedPot = false;
+
+    @Rule(categories = {SLSA, RuleCategory.FEATURE})
+    public static boolean stackableVehicles = false;
 }

src/main/java/com/github/zly2006/carpetslsaddition/mixin/item/ItemInstanceMixin.java

@@ -0,0 +1,40 @@
+package com.github.zly2006.carpetslsaddition.mixin.item;
+
+import com.github.zly2006.carpetslsaddition.SLSCarpetSettings;
+import net.minecraft.world.item.BoatItem;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.ItemInstance;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.item.MinecartItem;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+/**
+ * 载具堆叠：让矿车/船的物品可以堆叠到 64。
+ *
+ * <p>26.1.2 的堆叠上限来自 {@code ItemInstance.getMaxStackSize()} 的 default 实现：
+ * 读取 {@code DataComponents.MAX_STACK_SIZE} 组件，默认 1（故矿车/船默认不堆叠）。
+ *
+ * <p>本 mixin 注入该 default 方法：规则 {@code stackableVehicles} 开启时，
+ * 若物品是矿车（{@link MinecartItem}）或船（{@link BoatItem}），返回 64。
+ * 由于堆叠上限变大，同类载具在拾取/整理时会自动合并，实现"自动堆叠"。
+ */
+@Mixin(ItemInstance.class)
+public interface ItemInstanceMixin {
+
+    @Inject(method = "getMaxStackSize", at = @At("HEAD"), cancellable = true)
+    private void stackableVehicles(CallbackInfoReturnable<Integer> cir) {
+        if (!SLSCarpetSettings.stackableVehicles) {
+            return;
+        }
+        if (!(this instanceof ItemStack stack)) {
+            return;
+        }
+        Item item = stack.getItem();
+        if (item instanceof MinecartItem || item instanceof BoatItem) {
+            cir.setReturnValue(64);
+        }
+    }
+}

src/main/resources/assets/slsaddition/lang/en_us.json

@@ -72,5 +72,7 @@
   "carpet.slsa.bot.respawned": "The bot %s's online time has been reset.",
   "carpet.slsa.bot.not_a_bot": "The player %s is not created by carpet sls addition, so you can't reset the online time.",
 
-  "carpet.slsa.block.deep_slate_core": "Deepslate Core"
+  "carpet.slsa.block.deep_slate_core": "Deepslate Core",
+  "carpet.rule.stackableVehicles.name": "Stackable vehicles",
+  "carpet.rule.stackableVehicles.desc": "Minecarts and boats can stack up to 64, auto-merging on pickup"
 }

src/main/resources/assets/slsaddition/lang/zh_cn.json

@@ -72,5 +72,7 @@
   "carpet.slsa.bot.respawned": "假人%s的在线时长已重置！",
   "carpet.slsa.bot.not_a_bot": "假人%s不是由Carpet SLS Addition生成的，所以你不能重置它的在线时间！",
 
-  "carpet.slsa.block.deep_slate_core": "深板岩核心"
+  "carpet.slsa.block.deep_slate_core": "深板岩核心",
+  "carpet.rule.stackableVehicles.name": "载具可堆叠",
+  "carpet.rule.stackableVehicles.desc": "矿车和船的物品可以堆叠到64，拾取时自动合并"
 }

src/main/resources/slsaddition.mixins.json

@@ -12,6 +12,7 @@
     "block.MixinDecoratedPotBlock",
     "block.MixinTrialSpawnerData",
     "block.MixinTrialSpawnerState",
+    "item.ItemInstanceMixin",
     "carpet.MixinEntityPlayerMPFake",
     "carpet.MixinPlayerCommand",
     "elytra.ItemAccessor",