Use indices instead of WorkTimeDatesInterface

Checking start/end dates are done very, very often in date calculations (often looping through every day in a date range). So I'd prefer more opaque code but less overhead.

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

@@ -17,7 +17,6 @@
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
 import ifcopenshell.util.date
-from ifcopenshell.util.data import WorkTimeDatesInterface
 
 
 class Usecase:
@@ -55,10 +54,12 @@ class Usecase:
         self.settings = {"work_time": work_time, "attributes": attributes or {}}
 
     def execute(self):
-        work_time_dates = WorkTimeDatesInterface(self.settings["work_time"])
         for name, value in self.settings["attributes"].items():
-            if name in ("Start", "Finish", "StartDate", "FinishDate"):
+            if name in ("Start", "StartDate"):
                 value = ifcopenshell.util.date.datetime2ifc(value, "IfcDate")
-                setattr(work_time_dates, name, value)
+                self.settings["work_time"][4] = value
+            elif name in ("Finish", "FinishDate"):
+                value = ifcopenshell.util.date.datetime2ifc(value, "IfcDate")
+                self.settings["work_time"][5] = value
             else:
                 setattr(self.settings["work_time"], name, value)