Timeline auto-scrolling is wonky

[jminor]

Something changed recently in the way Raven scrolls horizontally. It used to be possible to zoom and scroll so the playhead is off screen, but now the scroll position seems to automatically move or snap so the playhead is always visible.

This causes some odd behavior when dragging the playhead past about 2/3 of the window width. Specifically the playhead and scroll position zip ahead very quickly, making it difficult to place the playhead sometimes.

https://github.com/user-attachments/assets/c8518f5a-e423-418e-9e2d-7e61cb7f3cae