Add C/C++ and Scala environments

modules/dev/shell.nix

@@ -0,0 +1,16 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+with lib.my;
+let cfg = config.modules.dev.shell;
+in {
+  options.modules.dev.shell = {
+    enable = mkBoolOpt false;
+  };
+
+  config = mkIf cfg.enable {
+    user.packages = with pkgs; [
+      shellcheck
+    ];
+  };
+}