Mark files as viewed

Managing large pull requests can often be a time-consuming and challenging task, but a new feature that allows users to mark files as viewed aims to streamline the process. This feature helps reviewers easily track their progress by displaying the number of files viewed and remaining at the top of the pull request, allowing them to collapse files once reviewed. If any changes occur after a file has been marked, a "Changed since last view" badge ensures that reviewers are aware of updates. The development of this feature, credited to Product Designer @califa and Product Engineer @nplasterer, is intended to simplify the code review process, particularly for extensive pull requests.