feat(memory): declare 'memory' module

modules/memory/zram.nix

@@ -0,0 +1,11 @@
+{ config, lib, ... }:
+
+{
+  config = lib.mkIf config.memory.zram.enable {
+    zramSwap.enable = true;
+    boot.kernel.sysctl = {
+      "vm.swappiness" = lib.mkDefault 180;
+      "vm.page-cluster" = lib.mkDefault 0;
+    };
+  };
+}