Implement arithmetic formulas for cost value components

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

@@ -0,0 +1,18 @@
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"parent": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        value = self.file.create_entity("IfcCostValue")
+        if self.settings["parent"].is_a("IfcCostItem"):
+            values = list(self.settings["parent"].CostValues or [])
+            values.append(value)
+            self.settings["parent"].CostValues = values
+        elif self.settings["parent"].is_a("IfcCostValue"):
+            values = list(self.settings["parent"].Components or [])
+            values.append(value)
+            self.settings["parent"].Components = values
+        return value