Fix animation jank

[ericclemmons]

You can see my changes here:
https://github.com/peterp/cmdcmd/compare/main...ericclemmons:animate-from-window-frame?body=&expand=1

Demo:

demo.mp4

[peterp]

Holy smokes, that's amazing! I've invited you as a collaborator, so you should be able to open a PR

[peterp]

Fixed by #26.