perf: lazy open files improvements

In perf: open files lazily when serving content (!803 - merged) we attempted to improve performance of the zip reader by only opening files when they were actually needed. However, this caused 2022-07-14: Web pages are not loading properly (gitlab-com/gl-infra/production#7438 - closed) likely because of the reasons noted in !803 (comment 1026992862).

This issue is a follow-up conversation to see if we want to implement this in the future. For now, the changes are being reverted in !815 (closed) & !814 (closed)