### Summary Expanding/collapsing a diff on a file in large MRs is unnecessary slow even after the diff has been already fetched and loaded. The smaller MR is, the less noticeable the issue, but I tried on a large MR with the following summary: * 248 changes * 40 changes * 248 files edited Statistics for a particular file I tried with in this MR (though the same is true for all files in this MR): * +55 * -61 ### Steps to reproduce Load diff ("Changes" tab) for such large MR with a file that has a lot of changes. Click `˅` icon in front of the file's name if it is expanded (`˃` if the diff for file is collapsed). Loading diff or collapsing in my case took 2.6 seconds (see the screenshot). ### Example Project Merge Requests numbers 2 and 6 in GDK-generated version of CE. ### What is the current *bug* behavior? Expanding and collapsing a diff for a file takes way too long and is unexpected considering that the diff has already been fetched and rendered on the screen. ### What is the expected *correct* behavior? Collapsing/expanding should happen instantly. At least from the user experience point of view. ### Relevant logs and/or screenshots