Do not go through all directory files when bumping
Closes #127.
Before this patch, we were listing, reading and checking all the files (direct and in subdirs) we could find from the bump directory. This may be highly inefficient, especially when the directory contains a lot of files that will end up ignored from the Sorbet config.
After this patch, while we still list them all, we at least do not read and check them if they get ignored by the config.
@Morriar Just cleaning through our PRs: Can we merge this one?
No, as pointed in the issue it only moved the problem. I'll have to find a smarter way.
Superseded by https://github.com/Shopify/spoom/pull/322.