Speed up CI

[benthecarman]

We can probably do some more caching in CI to speed things up.

Would be best if we nix-ified it as well

[AnthonyRonning]

nix-ified it as well

We do this for a few of the servers right now and I have not figured out how to make it faster. We cache some of the nix stuff, but I think it pulls in all of the cargo files too. I think if we can cache those too, it could be faster. But right now it's like 15 minutes with the whole fedimint stack that it pulls in.

[benthecarman]

But right now it's like 15 minutes with the whole fedimint stack that it pulls in

fedimint's CI only takes a couple mins so it should be possible to get it pretty low