refactor(modules/hm): tidy up the modules

Should make further additions and refactors easier.

modules/hm/dev.nix

@@ -1,9 +1,4 @@
-{
-  pkgs,
-  lib,
-  config,
-  ...
-}:
+{ lib, config, ... }:
 let
   cfg = config.jhome.dev;
 in
@@ -11,12 +6,12 @@ in
   config =
     lib.flip lib.pipe
       [
-        lib.mkMerge
         (lib.mkIf (config.jhome.enable && cfg.enable))
+        lib.mkMerge
       ]
       [
         (lib.mkIf cfg.rust.enable {
-          home.packages = [ pkgs.rustup ] ++ cfg.rust.extraPackages;
+          home.packages = [ pkgs.rustup ] ++ devcfg.rust.extraPackages;
           # Background code checker (for Rust)
           programs.bacon = {
             enable = true;
@@ -31,8 +26,8 @@ in
         })
         {
           home = {
-            sessionVariables.MANPAGER = lib.optionalString cfg.neovimAsManPager "nvim -c 'Man!' -o -";
-            packages = cfg.extraPackages;
+            sessionVariables.MANPAGER = lib.optionalString devcfg.neovimAsManPager "nvim -c 'Man!' -o -";
+            packages = devcfg.extraPackages;
           };
 
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