flake, overlays: move stable and master overlays to host config

Defining the `stable` and `master` package overlays directly in `flake/hosts.nix` allows them to properly
inherit `config.nixpkgs.config` from the specific host.

flake/hosts.nix

@@ -9,8 +9,24 @@
 }:
 let
   vars = import ../vars.nix;
-  pkgsModule = {
-    nixpkgs = pkgsParams;
+  pkgsModule = { config, ... }: {
+    nixpkgs = lib.mkMerge [
+      pkgsParams
+      {
+        overlays = [
+          (final: _prev: {
+            stable = import inputs.nixpkgs-stable {
+              inherit (final.stdenv.hostPlatform) system;
+              inherit (config.nixpkgs) config;
+            };
+            master = import inputs.nixpkgs-master {
+              inherit (final.stdenv.hostPlatform) system;
+              inherit (config.nixpkgs) config;
+            };
+          })
+        ];
+      }
+    ];
   };
   hmModule = {
     home-manager = {

overlays/default.nix

@@ -1,16 +1,7 @@
 {
-  inputs,
   lib,
   ...
 }:
-let
-  mkPkgs = type: final: _prev: {
-    ${type} = import inputs."nixpkgs-${type}" {
-      system = final.stdenv.hostPlatform.system;
-      config.allowUnfree = true;
-    };
-  };
-in
 {
   flake.overlays = {
     modifications =
@@ -28,9 +19,5 @@ in
               "LANDLOCK_ACCESS_FS_READ_FILE | LANDLOCK_ACCESS_FS_READ_DIR | LANDLOCK_ACCESS_FS_EXECUTE"
           '';
       };
-  }
-  //
-    # this allows us to access specific version of nixpkgs
-    # by `pkgs.unstable`, `pkgs.stable` and `pkgs.master`
-    lib.genAttrs [ "stable" "unstable" "master" ] mkPkgs;
+  };
 }