feat: Add perArch option (#11)

Co-authored-by: isabel <[e-mail]>

README.md

···
   - `modules`: A list of modules that will be included in all the hosts of the given class.
   - `specialArgs`: A list of special arguments that will be passed to all the hosts of the given class.
 
+- `easy-hosts.perArch`: This provides you with the `arch` argument such that you can specify what architectures get which modules.
+  - `modules`: A list of modules that will be included in all the hosts of the given arch.
+  - `specialArgs`: A list of special arguments that will be passed to all the hosts of the given arch.
+
 - `easy-hosts.perTag`: This provides you with the `tag` argument such that you can specify what tags get which modules.
   - `modules`: A list of modules that will be included in all the hosts with the given tag.
   - `specialArgs`: A list of special arguments that will be passed to all the hosts with the given tag.

flake-module.nix

···
         description = "Per class settings";
       };
 
+      perArch = mkOption {
+        default = _: {
+          modules = [ ];
+          specialArgs = { };
+        };
+        defaultText = ''
+          arch: {
+            modules = [ ];
+            specialArgs = { };
+          };
+        '';
+
+        type = types.functionTo (
+          types.submodule {
+            options = mkBasicParams "Per arch";
+          }
+        );
+
+        example = literalExpression ''
+          arch: {
+            modules = [
+              { system.nixos.label = arch; }
+            ];
+
+            specialArgs = { };
+          }
+        '';
+
+        description = "Per arch settings";
+      };
+
       perTag = mkOption {
         default = _: {
           modules = [ ];

lib.nix

···
           # memoize the class and perClass values so we don't have to recompute them
           perClass = easyHostsConfig.perClass hostConfig.class;
           perTag = builtins.map (easyHostsConfig.perTag) hostConfig.tags;
+          perArch = builtins.map (easyHostsConfig.perTag) hostConfig.arch;
           class = redefineClass easyHostsConfig.additionalClasses hostConfig.class;
         in
         toHostOutput {
···
                 hostConfig.modules
                 easyHostsConfig.shared.modules
                 perClass.modules
+                perArch.modules
               ]
               ++ (builtins.map ({ modules, ... }: modules) perTag)
             );
···
                 hostConfig.specialArgs
                 easyHostsConfig.shared.specialArgs
                 perClass.specialArgs
+                perArch.specialArgs
               ]
               ++ (builtins.map ({ specialArgs, ... }: specialArgs) perTag)
             );