take some inspiration from NixOS for different fetchers, mirrors, and so on.

NixOS has quite a few fetchers for different VCS systems as well as mirrored sites:

It might be worthwhile to spend some time understanding what they are doing there and get some inspiration. Some systems, such as GitHub, apparently do not return hashes in a consistent way per release, but it differs, so hashes that are used by NixOS are computed in a different way.

The NixOS fetchers have support for downloading from mirrors (example: sourceforge) and have supporting syntax in the Nix files for it, for example:

```
url = "mirror://sourceforge/scummvm/lure-${version}.zip";
```
which would automatically grab a mirror from the list of defined mirrors.

There are also some fetchers that are a bit more obscure bit which might be fun or useful to add.