test: add Symbol.iterator support to createMockFileList

Add iterator implementation to createMockFileList so the mock FileList can be
used with for...of loops and spread operations, ensuring full compatibility
with the iterable FileList interface.

src/utils/__tests__/litegraphTestUtils.ts

@@ -180,7 +180,10 @@ export function createMockFileList(files: File[]): FileList {
   const fileList = {
     ...files,
     length: files.length,
-    item: (index: number) => files[index] ?? null
+    item: (index: number) => files[index] ?? null,
+    [Symbol.iterator]: function* () {
+      yield* files
+    }
   }
   return fileList as FileList
 }