refactor(nixos): move nixosSystem config to lib

Moves the nixosSystem configuration logic to a library function for reuse.

modules/configurations/nixos.nix

@@ -1,44 +1,9 @@
-{
-  config,
-  lib,
-  inputs,
-  ...
-}:
+{ config, ... }:
 let
-  inherit (lib.trivial) pipe;
-  inherit (lib.attrsets) filterAttrs mapAttrs';
-  inherit (lib.strings) removePrefix hasPrefix;
+  inherit (cfg.lib) extractConfigurations;
   cfg = config.flake;
-  prefix = "nixos/";
   hosts = cfg.hostSpec.hosts or { };
-  mkSystem =
-    name: value:
-    let
-      hostName = removePrefix prefix name;
-      hostConfig = value;
-      flakeConfig = config;
-    in
-    {
-      name = hostName;
-      value = lib.nixosSystem {
-        specialArgs = {
-          inherit
-            inputs
-            hostName
-            hostConfig
-            flakeConfig
-            ;
-        };
-        modules = [
-          cfg.profiles.nixos.common
-          (value.extraCfg or { })
-        ] ++ (value.profiles or [ ]);
-      };
-    };
 in
 {
-  flake.nixosConfigurations = pipe hosts [
-    (filterAttrs (name: _: hasPrefix prefix name))
-    (mapAttrs' mkSystem)
-  ];
+  flake.nixosConfigurations = extractConfigurations "nixos/" hosts;
 }