File size doesn't update while playing a file that's still growing on disk

[mertemr]

Syncplay only reads the file size once, when the file starts playing. If the file keeps growing on disk after that (e.g. it's still being downloaded in the background), the size shown to other users never updates, even after the download finishes.

To reproduce:

1. Start playing a file that isn't fully downloaded yet and keeps growing while you play it
2. Check the file size shown to other room members
3. It stays the same for the whole session, even after the file is complete

Expected: file size should reflect what's actually on disk, not just the size at the moment playback started.

Syncplay: master