UserStorageError: failed to upsert user storage for path 'multichain_accounts_groups.78'. HTTP error message: undefined, error: rate limit exceeded

Sentry Issue: [METAMASK-XT2R](https://metamask.sentry.io/issues/6966285057/?referrer=github_integration)

```
UserStorageError: failed to upsert user storage for path 'multichain_accounts_groups.78'. HTTP error message: undefined, error: rate limit exceeded
at new UserStorageError (node_modules/@metamask/profile-sync-controller/dist/sdk/errors.cjs:27:1)
at _UserStorage_upsertUserStorage (node_modules/@metamask/profile-sync-controller/dist/sdk/user-storage.cjs:109:1)
at exports.UserStoragesetItem (node_modules/@metamask/profile-sync-controller/dist/sdk/user-storage.cjs:47:1)
at UserStorageController.performSetStorage (node_modules/@metamask/profile-sync-controller/dist/controllers/user-storage/UserStorageController.cjs:191:1)
at (node_modules/@metamask/account-tree-controller/dist/backup-and-sync/user-storage/network-operations.cjs:127:1)
...
(5 additional frame(s) were not displayed)
```

Start with the Sentry trace and inspect the referenced UserStorageController.performSetStorage and @metamask/profile-sync-controller user-storage calls, noting that the trace points to built package files rather than repository sources. Determine the expected handling for the rate-limit response and define completion criteria before changing code; the issue currently provides no expected behavior or named test.

Written by the indexing model from the issue text.