zvfs: 重构核心读写逻辑并新增 POSIX hook；引入目录元数据与伪 fd；分离创建、打开、关闭、删除的逻辑；

zvfs.old/zvfs.json

@@ -0,0 +1,17 @@
+{
+  "subsystems": [
+    {
+      "subsystem": "bdev",
+      "config": [
+        {
+          "method": "bdev_malloc_create",
+          "params": {
+            "name": "Malloc0",
+            "num_blocks": 32768,
+            "block_size": 512
+          }
+        }
+      ]
+    }
+  ]
+}