flake: add scipy to dependencies

scipy relies on libstdc++.so and cannot be used directly with venv in nix environment. adding it to buildInputs solves this issue.

flake.nix

@@ -18,10 +18,11 @@
       devShells.default = pkgs.mkShell {
         name = "python-venv";
         venvDir = "./.venv";
-        buildInputs = [
+        buildInputs = with pythonPackages; [
-          pythonPackages.python
+          python
-          pythonPackages.venvShellHook
+          venvShellHook
-          pythonPackages.numpy
+          scipy
+          numpy
         ];
 
         postVenvCreation = ''
@@ -35,4 +36,4 @@
         '';
       };
     });
-}
+}