[Feature Request]: Query video duration in playlists under a certain length

### Guidelines

- [x] I have searched the issue tracker for [open](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aopen+is%3Aissue) and [closed](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+is%3Aclosed) issues 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.

### Problem Description

Right now, if you have too many subscriptions FreeTube will use RSS to get video details, which does not include video duration. Adding one of these RSS videos to a playlist will still not re-query the duration. This makes great features like sorting by duration (#5627) unusable unless you manually start each video, which in turn makes the "remove watched videos" feature unusable.

### Proposed Solution

I'm proposing that so long as a playlist has under n videos (as determined by you guys, idk where rate limiting kicks in), details such as duration should be queried when the playlist is opened.

### Alternatives Considered

Alternatively, the action of adding a video to a playlist could trigger re-querying the details for that specific video.

### Issue Labels

ease of use improvement, improvement to existing feature, display more information to user, new feature, visual improvement

### Additional Information

_No response_

No files, tests, or entry points are named. Trace how playlists open and how RSS-provided videos are represented, then determine where duration details could be queried without exceeding the chosen playlist limit. Done means playlist videos under that limit have usable durations for duration sorting and watched-video removal.

Written by the indexing model from the issue text.