refactor: change to litterate config

Configuration is now held by the `.org` files. All `.nix` files are
tangled from the org-mode files.

modules/nix-config.nix

@@ -1,5 +1,5 @@
-{...}: let
-  cacheSettings = {
+let
+  cacheSettings = rec {
     substituters = [
       "https://phundrak.cachix.org?priority=10"
       "https://nix-community.cachix.org?priority=20"
@@ -10,28 +10,22 @@
       "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
       "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
     ];
+    commonConf = {
+      extra-trusted-public-keys = trustedPublicKeys;
+      extra-substituters = substituters;
+      extra-experimental-features = ["nix-command" "flakes"];
+      http-connections = 128;
+    };
   };
 in {
-  flake-file.nixConfig = {
-    extra-trusted-public-keys = cacheSettings.trustedPublicKeys;
-    extra-substituters = cacheSettings.substituters;
-    extra-experimental-features = ["nix-command" "flakes"];
-    http-connections = 128;
-  };
-
-  flake.nixConfig = {
-    extra-trusted-public-keys = cacheSettings.trustedPublicKeys;
-    extra-substituters = cacheSettings.substituters;
-    extra-experimental-features = ["nix-command" "flakes"];
-    http-connections = 128;
-  };
-
+  flake-file.nixConfig = cacheSettings;
+  flake.nixConfig = cacheSettings;
   flake.modules.nixos.nix-cache-settings = {
     nix.settings = {
-      substituters = cacheSettings.substituters;
+      inherit (cacheSettings) substituters;
       trusted-public-keys = cacheSettings.trustedPublicKeys;
-      http-connections = 128;
       experimental-features = ["nix-command" "flakes"];
+      http-connections = 128;
     };
   };
 }