fix: module args of home-manager portable configs

Type-check such configs as modules ("moduleType") rather than as
functions evaluating to attribute sets ("functionTo attrs").  This
ensures that they get invoked with all expected module arguments
("pkgs", "lib", etc.).

Update ./examples/hmOnly so that the testuser config references the pkgs
module arg, thus testing that the switch to moduleType works as
intended.

Closes #119

examples/hmOnly/home/users/testuser.nix

@@ -1,11 +1,13 @@
-{ suites, ... }:
+{ pkgs, suites, ... }:
 let
   name = "Test User";
   email = "[email protected]";
 in
 {
   imports = suites.shell;
 
+  home.packages = [ pkgs.hello ];
+
   programs.browserpass.enable = true;
   programs.starship.enable = true;
   programs.git = {

src/mkFlake/options.nix

@@ -94,7 +94,7 @@ let
     description = "nix flake";
   };
 
-  userType = with types; pathToOr (functionTo attrs) // {
+  userType = with types; pathToOr moduleType // {
     description = "HM user config";
   };