Feature Request: Cache nix builds on a public cache server?

[Azeirah]

Prerequisites

• I am running the latest code. Mention the version if possible as well.
• I carefully followed the README.md.
• I searched using keywords relevant to my issue to make sure that I am creating a new issue that is not already open (or closed).
• I reviewed the Discussions, and have a new and useful enhancement to share.

Feature Description

Publish builds of llama.cpp binaries to the public Nix binary cache https://cache.nixos.org/

Motivation

There's a nix flake that I think is primarily used for github actions and automation, which makes sense because Nix is great for CI and development environments and such!

But I use NixOS as my primary OS, and Nix is actually one of the platforms where it's easy to install llama.cpp with rocm support because of its declarative nature.

But every single time I update llama.cpp, I am rebuilding the entire project from scratch, even though I don't have any compiler option overrides or what have you.

Nix has a public binary cache https://cache.nixos.org/, so perhaps it'd be nice to publish the builds there?

Possible Implementation

I'm not super sure about how this would work exactly, but I think it should be a github action that publishes the builds to the cache.

[Azeirah]

Looking through the nix flake history, I saw that there is a cache configured for Nix.

https://github.com/ggml-org/llama.cpp/blob/198ed7ebfc89b8f2b35a8b1655d57bfb57530c1a/flake.nix

[Azeirah]

I configured the cache as described by the instructions in the flake, but it's still building llama-cpp-rocm-0.0.0 from scratch on my machine. Is this because the rocm build isn't cached?