[wip] fix scroll for big datasets

[severo]

see #241

[severo]

fyi @platypii:

it works :)

Screencast.From.2025-12-17.00-32-10.mp4

As you see, still a detail with the first cell being below the header in some configurations. I'll fix it tomorrow.

BUT, I just discovered that we also have to handle the horizontal scroll (we cannot focus the cell horizontally without also scrolling vertically, which breaks the virtual scroll)

Screencast.From.2025-12-17.00-35-35.mp4

After doing the horizontal scrolling, I think we will be able to test manually to ensure it's usable as expected, and I'll add unit tests...

[severo]

^ accidental click on "Close with comment"

[severo]

Tasks:

• under a threshold (< 17M pixels, first limit with Firefox), don't use a virtual domain, just use the scroll, as before
• above the threshold, handle better some details:
  • change in the number of rows
  • use a non-linear scroll? if the scroll gesture is less than a threshold (5% of the scrollbar height), consider it local, otherwise, global