Add linting, formatting, and CI

- Add deadnix, nixfmt, and statix to flake inputs
- Add formatter output to flake for nix fmt support
- Add deadnix, nixfmt, statix to Home Manager packages
- Format all nix files with nixfmt
- Add GitHub Actions workflow for CI validation
- Support x86_64-darwin in formatter

modules/hosts/nixos/hetznix01/post-install/containers/emqx.nix

@@ -1,6 +1,8 @@
-{ config, username, ... }: let
+{ config, username, ... }:
+let
   volume_base = "/var/lib/emqx";
-in {
+in
+{
   # Based on docs at https://docs.emqx.com/en/emqx/latest/deploy/install-docker.html
   virtualisation.oci-containers.containers = {
     "emqx" = {