♻️ consolidate nix configs

nix/modules/builder/default.nix

@@ -0,0 +1,30 @@
+_: {
+  nix = {
+    distributedBuilds = true;
+    buildMachines = [
+      {
+        hostName = "plato";
+        systems = [ "x86_64-linux" "aarch64-linux" ];
+        maxJobs = 6;
+        supportedFeatures = [ "benchmark" "big-parallel" "kvm" ];
+      }
+    ];
+    extraOptions = ''
+      builders-use-substitutes = true
+    '';
+    linux-builder = {
+      enable = true;
+      ephemeral = true;
+      maxJobs = 4;
+      speedFactor = 2;
+      config = {
+        virtualisation = {
+          darwin-builder = {
+            memorySize = 8 * 1024;
+          };
+          cores = 4;
+        };
+      };
+    };
+  };
+}