Fix reticulum build: add sourceRoot for PyPI package

overlays/reticulum.nix

@@ -12,6 +12,11 @@ in
         inherit version;
         sha256 = "554814231c237b9caacf8df669312e57dd7d3f84b6d4810125087d1a79a75d75";
       };
+      sourceRoot = "rns-${version}";
+      postUnpack = ''
+        echo "=== RNS source structure ==="
+        find . -maxdepth 3 -type d | head -20
+      '';
       propagatedBuildInputs = with pyPkgs; [ cryptography pyserial ];
       doCheck = false;
       pythonImportsCheck = [ "RNS" ];