we need to use an _even older_ version of ghc than we're using now and
modern-uri doesn't seem particularly amenable to that.

network-uri is perfectly fine, anyway.

quite possibly both of these interfaces are wrong
may want to ponder them for a moment before proceeding

Simplistic implementation of download

Closes #1

See merge request !1

And it only tells us what cabal tells us later, packages are broken...

fresh start

reduce closure size etc

Tell cabal to configure zlib a certain way when building it, making its build
errors go away without changing our own cabal package configuration.

`cabal list-bins ...` might output some garbage before outputting the path, so
this breaks :/  Also why do it the hard way when we can do it the easy way!

It fails because we didn't finish implementing it yet, and also because there
might be some more bugs.

Co-Authored-By:  <shae@private.storage>

I almost used it to narrow these two dependencies to library-only but it turns
out to not make much difference so it doesn't seem worth the extra complexity
now.

However, having access to the library might prove useful in the future.

Each generated with `cabal2nix https://.../` and then mangled by alejandro

somehow I forgot to write the test for this bit first
too exciting to actually be implementing a downloader I suppose