modules: refactor common

move common into directory

modules/nixos/common/users.nix

@@ -0,0 +1,22 @@
+{ inputs, lib, ... }:
+
+let
+  usersDir = "${toString inputs.self}/users";
+  userImports =
+    let
+      toUserPath = f: usersDir + "/${f}";
+      onlyUserFiles = x:
+        lib.hasSuffix ".nix" x &&
+        x != "lib.nix"
+      ;
+      userDirEntries = builtins.readDir usersDir;
+      userFiles = builtins.filter onlyUserFiles (lib.attrNames userDirEntries);
+    in
+    builtins.map toUserPath userFiles;
+in
+{
+  imports = userImports;
+
+  # No mutable users
+  users.mutableUsers = false;
+}