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;
 }