Pinch zoom doesn't work on Wayland

**Describe the bug**
Pinch zoom does not change the zoom delta.

**To Reproduce**
Steps to reproduce the behavior:
1. use the zoom_delta from InputState for zooming
2. try to pinch zoom -> zoom_delta is still 1

I have confirmed normal zoom scrolling ctrl + scroll works fine on my touchpad.
Pinch zoom also works fine in other apps (in my case Zen Browser).

**Expected behavior**
Pinch zoom should change the zoom_delta appropriately.

**Desktop (please complete the following information):**
- OS: Linux (NixOS unstable)
- Desktop: Wayland (Niri)
- Version 0.36.1 (reproducible on main)

**Additional Context**
This also applies to zoom_delta_2d.

Start by reproducing the issue on Linux Wayland with a touchpad, then trace how InputState computes zoom_delta and zoom_delta_2d. Done means pinch gestures change both zoom values appropriately while the existing ctrl+scroll behavior continues to work.

Written by the indexing model from the issue text.