[Feature Request]: Add fallback behavior for RSS ratelimiting

### Guidelines

- [x] I have [searched the issue tracker for open and closed issues](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+sort%3Arelevance-desc) that are similar to the feature request I want to file, without success.
- [x] I have searched the [documentation](https://docs.freetubeapp.io/) for information that matches the description of the feature request I want to file, without success.
- [x] This issue contains only one feature request.
- [x] I have read and agree to follow the [rules](https://docs.freetubeapp.io/community/rules/).

### Problem Description

When YouTube is having a RSS outage on the RSS feeds users are met with the following on our Subscription page

* Your subscribed channels currently does not have any videos
* Channels with errors

While technically correct it isnt very user friendly.

### Proposed Solution

Show the videos that were listed before refreshing the subscriptions and show a toast that mentions that fetching failed instead of the things listed above

### Alternatives Considered

None.

### Issue Labels

ease of use improvement, display more information to user, visual improvement

### Additional Information

_No response_

Commencez par la page Subscription et suivez la manière dont les échecs d’actualisation RSS produisent actuellement les messages empty-subscription et channel-error. Vérifiez comment les vidéos précédemment listées et les notifications toast sont gérées. C’est terminé lorsque les vidéos précédentes restent visibles après un échec RSS et qu’une notification toast indique que la récupération a échoué.

Rédigé par le modèle d'indexation à partir du texte de l'issue.