fix serialization of numpy scalars in job XML under numpy 2

numpy 2 changed repr(np.float64(1e-06)) to 'np.float64(1e-06)', so values
taken from lin_range() ended up unparsable in the job file: the result
script failed with "could not convert string to float". Description items
and state times are now converted to builtin types before writing.

tests/test_Experiment.py

@@ -42,6 +42,34 @@ class TestExperimentPhase(unittest.TestCase):
         e.rf_pulse(length=1e-6, phase=-90, source=0)
         self.assertEqual(phase_of_state(e.state_list.list[0]), 270.0)
 
+    def test_numpy_scalars_in_description(self):
+        """Test that description items with numpy scalars (e.g. from lin_range)
+        are written as plain numbers so the result script can parse them again."""
+        import numpy as np
+        from damaris.tools.ranges import lin_range
+        e = Experiment()
+        e.set_description("tau", lin_range(1e-6, 3e-6, 1e-6)[0])
+        e.set_description("n", np.int64(42))
+        xml = e.write_xml_string()
+        items = {key: (typ, text)
+                 for key, typ, text in
+                 re.findall(r'<item key="([^"]+)" type="([^"]+)">([^<]*)</item>', xml)}
+        self.assertEqual(items["tau"][0], "Float")
+        self.assertEqual(items["n"][0], "Int")
+        self.assertEqual(float(items["tau"][1]), 1e-6)
+        self.assertEqual(int(items["n"][1]), 42)
+
+    def test_numpy_scalar_state_times(self):
+        """Test that numpy scalar times do not end up as np.float64(...) in the XML."""
+        import numpy as np
+        e = Experiment()
+        e.wait(np.float64(1e-6))
+        e.state_start(np.float64(2e-6))
+        xml = e.write_xml_string()
+        self.assertNotIn("np.float64", xml)
+        self.assertIn('<state time="1e-06"/>', xml)
+        self.assertIn('<state time="2e-06">', xml)
+
 
 if __name__ == "__main__":
     unittest.main()