bulk editor actions on custom galleries cause preview images to display at incorrect dimensions

[beatricelucaci]

Describe the bug
When applying bulk editor actions on custom grid galleries, the preview images appear excessively large.
This happens because the image dimensions are being calculated incorrectly based on the grid system.
For normal galleries, images are resized properly (e.g., 1000px to 250px), but for custom grid galleries, the calculation should be based on the number of grid squares (1 square = 125px). Instead, the width is being set to 125px multiplied by the image's original width, resulting in oversized previews.

https://support.wpchill.com/conversation/24207?folder_id=81