feat(nixos): improve nix configuration and tmp handling

- Reformatted function parameters to enhance readability.
- Added `build-dir = "/var/tmp"` to nix settings for better build management.
- Removed redundant `TMPDIR` environment variable for nix-daemon in systemd services.

modules/nixos/nix/default.nix

@@ -59,15 +59,16 @@ in
         users = [
           "root"
           config.metacfg.user.name
-        ] ++ optional config.services.hydra.enable "hydra";
+        ]
+        ++ optional config.services.hydra.enable "hydra";
         extra-substituters = cfg.extra-substituters;
       in
       {
         package = cfg.package;
 
-        settings =
-          {
+        settings = {
           experimental-features = "nix-command flakes";
+          build-dir = "/var/tmp";
           http-connections = 50;
           warn-dirty = false;
           log-lines = 50;
@@ -78,10 +79,12 @@ in
 
           substituters = [
             cfg.default-substituter.url
-            ] ++ (mapAttrsToList (name: value: name) extra-substituters);
+          ]
+          ++ (mapAttrsToList (name: value: name) extra-substituters);
           trusted-public-keys = [
             cfg.default-substituter.key
-            ] ++ (mapAttrsToList (name: value: value.key) extra-substituters);
+          ]
+          ++ (mapAttrsToList (name: value: value.key) extra-substituters);
 
         }
         // (lib.optionalAttrs config.metacfg.tools.direnv.enable {

modules/nixos/services/base/default.nix

@@ -1,7 +1,8 @@
-{ config
-, lib
-, pkgs
-, ...
+{
+  config,
+  lib,
+  pkgs,
+  ...
 }:
 with lib;
 with lib.metacfg;
@@ -188,7 +189,6 @@ in
     virtualisation.libvirtd.enable = lib.mkDefault true;
 
     boot.tmp.useTmpfs = true;
-    systemd.services.nix-daemon.environment.TMPDIR = "/var/tmp";
 
     services.fstrim.enable = true;
   };