refactor(nixos): use new persistDirs option and remove environment.persistence where possible

modules/nixos/default.nix

@@ -0,0 +1,46 @@
+{ lib, config, ... }:
+let
+  inherit (lib) mkOption;
+  inherit (lib.types)
+    listOf
+    str
+    coercedTo
+    submodule
+    ;
+  rootDir = submodule {
+    options = {
+      directory = mkOption { type = str; };
+      user = mkOption {
+        type = str;
+        default = "root";
+      };
+      group = mkOption {
+        type = str;
+        default = "root";
+      };
+      mode = mkOption {
+        type = str;
+        default = "0755";
+      };
+    };
+  };
+in
+{
+  options = {
+    persistDirs = mkOption {
+      type = listOf (coercedTo str (d: { directory = d; }) rootDir);
+      default = [ ];
+    };
+  };
+
+  config = {
+    # Helper options
+    environment.persistence."/persist".directories = config.persistDirs;
+
+    # Global options
+    persistDirs = [
+      "/var/lib/systemd"
+      "/var/lib/nixos"
+    ];
+  };
+}