Cache and add refresh command

[jacksongoode]

This adds a refresh command so that people are able to get new changes from the repository source. I also simplified the zip extractor.

[github-advanced-security]

clippy found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[jacksongoode]

@ryanccn Hi, just seeing if this would be possible to be merged in? I've been using it regularly and there haven't been any issues.

[ryanccn]

I don't think having a dependency on Git and using it for incremental updates makes sense, since nyoom should ideally be as independent from OS dependencies as possible (which is why the unzip functionality is in Rust!). nyoom's source scheme is modeled after Nix's flake references, and with Nix, flakes from known Git providers such as GitHub are downloaded as archives, since

These are downloaded as tarball archives, rather than through Git. This is often much faster and uses less disk space since it doesn't require fetching the entire history of the repository. On the other hand, it doesn't allow incremental fetching (but full downloads are often faster than incremental fetches!).

This is why downloading sources as archives and re-fetching them to update makes more sense IMO. I appreciate the loads of work you've put into this PR; however, I don't think I agree with its premise so I won't be able to merge it at the end of the day.