add short dict and getter in HS

src/Model/HydraulicStructures/HydraulicStructures.py

@@ -233,6 +233,9 @@ class HydraulicStructure(SQLSubModel):
     def basic_structures(self):
         return self._data.copy()
 
+    def basic_structure(self, index: int):
+        return self._data[index]
+
     def add(self, index: int):
         value = NotDefined(status=self._status)
         self._data.insert(index, value)