fix/touchpad scrolling lag

When using touchpad on a laptop, the scrolling doesn't work well, only moving upon large and fast movement. Thus changed the event catching to better represent the movement. <!-- This is an auto-generated description by cubic. --> --- ## Summary by cubic Fixes laggy touchpad scrolling in `TVarGrid` by accumulating wheel deltas into line-based scroll steps. Scrolling now feels smooth and consistent across devices and LCL versions. - Bug Fixes - Added `FWheelAccumulator` to collect `WheelDelta` and scroll only when a full step (120) is reached. - Correctly maps steps to lines using `Mouse.WheelScrollLines` or `VisibleRowCount`, with proper handling for `< 1.8.0` and `>= 1.8.0` LCL branches. ^{Written for commit 89c48594e89ca3d2a3613647a48e9bafd24724ba. Summary will update on new commits.} <a href="https://cubic.dev/pr/transmission-remote-gui/transgui/pull/1575?utm_source=github" target="_blank" rel="noopener noreferrer" data-no-image-dialog="true"><picture><source media="(prefers-color-scheme: dark)" srcset="https://www.cubic.dev/buttons/review-in-cubic-dark.svg"><source media="(prefers-color-scheme: light)" srcset="https://www.cubic.dev/buttons/review-in-cubic-light.svg"><img alt="Review in cubic" src="https://www.cubic.dev/buttons/review-in-cubic-dark.svg"></picture></a> <!-- End of auto-generated description by cubic. -->