test: add coverage for editorStore methods and file system operations

vitest.setup.ts

@@ -17,7 +17,10 @@ vi.mock("@tauri-apps/api/core", () => ({
     if (command in mockInvokeResults) {
       const result = mockInvokeResults[command];
       if (result instanceof Error) {
-        return Promise.reject(result);
+        const err = result;
+        return Promise.resolve().then(() => {
+          throw err;
+        });
       }
       return Promise.resolve(result);
     }