feat: 添加 SkinBridge 皮肤兼容

src/main/java/cn/infstar/essentialsC/skinbridge/SkinBridgeGateway.java

@@ -0,0 +1,18 @@
+package cn.infstar.essentialsC.skinbridge;
+
+import org.bukkit.entity.Player;
+
+interface SkinBridgeGateway {
+
+    GeneratedSkin generateSkin(String skinUrl, SkinModel model) throws Exception;
+
+    void applySkin(Player player, GeneratedSkin skin) throws Exception;
+}
+
+enum SkinModel {
+    CLASSIC,
+    SLIM
+}
+
+record GeneratedSkin(String value, String signature) {
+}