Box/lasso selection should be compatible with PTZ

Box selection with the Select tool and Path tool doesn't follow the canvas when panning (via the mouse vertical/horizontal scroll wheel) or zooming (with Ctrl + or Ctrl -). The starting point of the rectangle should be locked down to the canvas location, not follow the viewport. This works correctly with the auto-panning feature (dragging the box selection off the edges of the viewport), so that code can be referenced. The actual box selection must still be rounded to viewport coordinates so the box selection is drawn cleanly (without fuzzy antialiasing). The video below shows the incorrect present behavior.

https://github.com/user-attachments/assets/6687128d-0123-4feb-bd10-88c36440971d

Discussion in this Discord thread: https://discord.com/channels/731730685944922173/1321358747133677599

Start with the Select tool and Path tool box-selection behavior, then reproduce the issue while panning with the mouse scroll wheel and zooming with Ctrl + or Ctrl -. Use the existing auto-panning behavior as the reference. Done means the rectangle's starting point remains locked to its canvas location while the selection stays rounded to viewport coordinates for clean rendering.

Written by the indexing model from the issue text.