New feature to toggle default project unit assignment

src/ifcopenshell-python/ifcopenshell/api/unit/unassign_unit.py

@@ -0,0 +1,17 @@
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"units": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        unit_assignment = self.file.by_type("IfcUnitAssignment")
+        if not unit_assignment:
+            return
+        unit_assignment = unit_assignment[0]
+        units = set(unit_assignment.Units or [])
+        units = units - set(self.settings["units"])
+        if units:
+            unit_assignment.Units = list(units)
+        return unit_assignment