Add hydra as a distributed build machine.

nix/configuration/hosts/hydra/default.nix

@@ -24,4 +24,9 @@
   me.zsh.enable = true;
   me.wireguard.activated = [ ];
   me.wireguard.deactivated = [ ];
+
+  # Trust this key so nix running as root can ssh into hydra.
+  users.users.talexander.openssh.authorizedKeys.keys = [
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIB/IlYTQ0M5pFN5tdoswh37CDl/gbULI3h+SsKXCansh talexander@odo"
+  ];
 }

nix/configuration/hosts/hydra/optimized_build.nix

@@ -8,7 +8,17 @@
   imports = [ ];
 
   config = lib.mkMerge [
-    { }
+    {
+      nix.settings.system-features = lib.mkForce [
+        "gccarch-znver4"
+        "gccarch-x86-64-v3"
+        "gccarch-x86-64-v4"
+        "benchmark"
+        "big-parallel"
+        # "kvm"
+        # "nixos-test"
+      ];
+    }
     (lib.mkIf (!config.me.buildingIso) {
       nix.settings.system-features = lib.mkForce [
         "gccarch-znver4"