Implement feature for manipulating cost values, with support for calculation of subtotals

src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_value.py

@@ -0,0 +1,16 @@
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"cost_item": None, "ifc_class": "IfcQuantityCount"}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        value = self.file.create_entity("IfcCostValue")
+        values = list(self.settings["cost_item"].CostValues or [])
+        values.append(value)
+        self.settings["cost_item"].CostValues = values
+        return value