fix list_guest_directory for varying guest OS attributes

FileInfo attributes (owner, modificationTime, size, type) vary across
guest OS types. Use getattr with defaults to prevent AttributeError
when these optional fields are missing.

src/esxi_mcp_server/mixins/guest_ops.py

@@ -308,16 +308,17 @@ class GuestOpsMixin(MCPMixin):
         except vim.fault.FileNotFound:
             raise ValueError(f"Directory not found: {guest_path}") from None
 
-        return [
-            {
+        results = []
+        for f in listing.files:
+            mod_time = getattr(f, "modificationTime", None)
+            results.append({
                 "name": f.path,
-                "size": f.size,
-                "type": f.type,
-                "owner": f.owner,
-                "modified": f.modificationTime.isoformat() if f.modificationTime else None,
-            }
-            for f in listing.files
-        ]
+                "size": getattr(f, "size", None),
+                "type": getattr(f, "type", None),
+                "owner": getattr(f, "owner", None),
+                "modified": mod_time.isoformat() if mod_time else None,
+            })
+        return results
 
     @mcp_tool(
         name="create_guest_directory",