cynthion: make udev rules accessible

Copy udev rules to an output path searched by the NixOS option
services.udev.packages.

pkgs/development/python-modules/cynthion/default.nix

@@ -23,6 +23,7 @@
 
   # tests
   pytestCheckHook,
+  udevCheckHook,
 }:
 buildPythonPackage rec {
   pname = "cynthion";
@@ -44,6 +45,8 @@ buildPythonPackage rec {
       --replace-fail 'dynamic = ["version"]' 'version = "${version}"'
   '';
 
+  nativeBuildInputs = [ udevCheckHook ];
+
   build-system = [
     setuptools
   ];
@@ -72,6 +75,13 @@ buildPythonPackage rec {
 
   pythonImportsCheck = [ "cynthion" ];
 
+  # Make udev rules available for NixOS option services.udev.packages
+  postInstall = ''
+    install -Dm444 \
+      -t $out/lib/udev/rules.d \
+      build/lib/cynthion/assets/54-cynthion.rules
+  '';
+
   meta = {
     description = "Python package and utilities for the Great Scott Gadgets Cynthion USB Test Instrument";
     homepage = "https://github.com/greatscottgadgets/cynthion";