feat(memory): declare 'memory' module

modules/memory/default.nix

@@ -0,0 +1,19 @@
+{ lib, ... }:
+
+{
+  imports = [
+    ./oom.nix
+    ./zram.nix
+  ];
+
+  options.memory = {
+    oom.enable = lib.mkOption {
+      default = false;
+      type = lib.types.bool;
+    };
+    zram.enable = lib.mkOption {
+      default = false;
+      type = lib.types.bool;
+    };
+  };
+}