规范化xml内容，并在xml中添加仿真设置，规范化版本号等内容，补充xml规范md文件

tests/test_system_xml_protocol.py

@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+import unittest
+from xml.etree import ElementTree as ET
+
+from app.main import ReactFlowProjectPayload, build_reactflow_system_xml
+
+
+class SystemXmlProtocolTests(unittest.TestCase):
+    def test_v1_xml_contains_simulation_and_stable_section_order(self) -> None:
+        project = ReactFlowProjectPayload(
+            name="protocol-test",
+            nodes=[
+                {
+                    "id": "cylinder_1",
+                    "type": "simulationComponent",
+                    "position": {"x": 12.5, "y": 24.0},
+                    "data": {
+                        "label": "source-cylinder",
+                        "componentType": "cylinder",
+                        "modelType": "cylinder",
+                        "ports": ["port_b"],
+                        "parameters": {"volume": 0.01, "p0": 35000000, "T0": 300},
+                    },
+                }
+            ],
+            edges=[],
+            simulation={
+                "t_start": 1.0,
+                "t_stop": 5.0,
+                "step": 0.2,
+                "max_step": 0.01,
+                "method": "BDF",
+            },
+        )
+
+        root = ET.fromstring(build_reactflow_system_xml(project))
+
+        self.assertEqual(root.tag, "System")
+        self.assertEqual(root.attrib["name"], "protocol-test")
+        self.assertEqual(root.attrib["schemaVersion"], "1")
+        self.assertEqual(root.attrib["unitSystem"], "SI")
+        self.assertEqual([child.tag for child in root], ["Simulation", "Components", "Connections"])
+
+        simulation = root.find("Simulation")
+        self.assertIsNotNone(simulation)
+        assert simulation is not None
+        self.assertEqual(
+            simulation.attrib,
+            {
+                "tStart": "1.0",
+                "tStop": "5.0",
+                "step": "0.2",
+                "maxStep": "0.01",
+                "method": "BDF",
+            },
+        )
+
+        component = root.find("./Components/Component")
+        self.assertIsNotNone(component)
+        assert component is not None
+        self.assertEqual(component.attrib["id"], "cylinder_1")
+        self.assertEqual(component.find("./Parameter[@name='p0']").attrib["value"], "35000000")
+
+
+if __name__ == "__main__":
+    unittest.main()