feat(tmp): declare 'tmp' module

modules/tmp/default.nix

@@ -0,0 +1,15 @@
+{ lib, config, ... }:
+
+{
+  options.tmp.enable = lib.mkOption {
+    default = config.host.highRam;
+    type = lib.types.bool;
+  };
+
+  config = lib.mkIf config.tmp.enable {
+    boot.tmp = {
+      useTmpfs = true;
+      tmpfsSize = "25%";
+    };
+  };
+}