modules/config: init new module

Signed-off-by: unexplrd <unexplrd@linerds.us>

modules/nixos/config/nix/common.nix

@@ -0,0 +1,39 @@
+{
+  pkgs,
+  lib,
+  ...
+}: {
+  nix = {
+    package = pkgs.lixPackageSets.latest.lix;
+    channel.enable = false;
+    daemonCPUSchedPolicy = "idle";
+    settings = {
+      experimental-features = [
+        "nix-command"
+        "flakes"
+        # for container in builds support
+        "auto-allocate-uids"
+        "cgroups"
+
+        # Enable the use of the fetchClosure built-in function in the Nix language.
+        "fetch-closure"
+
+        # Allow derivation builders to call Nix, and thus build derivations recursively.
+        "recursive-nix"
+
+        # Allow the use of the impure-env setting.
+        # "configurable-impure-env"
+      ];
+    };
+  };
+  # no longer need to pre-allocate build users for everything
+  nix.settings.auto-allocate-uids = lib.mkDefault true;
+  # Needs a patch in Nix to work properly: https://github.com/NixOS/nix/pull/13135
+  nix.settings.use-cgroups = true;
+
+  # for container in builds support
+  nix.settings.system-features =
+    if lib.versionAtLeast lib.version "25.05pre"
+    then ["uid-range"]
+    else lib.mkDefault ["uid-range"];
+}