New assign / unassign declaration usecase, minor code & formatting cleanup

src/ifcopenshell-python/ifcopenshell/api/sequence/add_work_time.py

@@ -0,0 +1,18 @@
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"work_calendar": None, "type": "WorkingTimes", "name": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        work_time = self.file.create_entity("IfcWorkTime", **{"Name": self.settings["name"]})
+        if self.settings["type"] == "WorkingTimes":
+            working_times = list(self.settings["work_calendar"].WorkingTimes or [])
+            working_times.append(work_time)
+            self.settings["work_calendar"].WorkingTimes = working_times
+        elif self.settings["type"] == "ExceptionTimes":
+            exception_times = list(self.settings["work_calendar"].ExceptionTimes or [])
+            exception_times.append(work_time)
+            self.settings["work_calendar"].WorkingTimes = exception_times
+        return work_time