specify exported api methods in __all__

It's py.types requirement, similar to 6e2edbf

Example issue without __all__:
import ifcopenshell
import ifcopenshell.api.project

# "create_file" is not exported from module "ifcopenshell.api.project"
ifcopenshell.api.project.create_file()

src/ifcopenshell-python/ifcopenshell/api/boundary/__init__.py

@@ -30,3 +30,10 @@ from .edit_attributes import edit_attributes
 from .remove_boundary import remove_boundary
 
 wrap_usecases(__path__, __name__)
+
+__all__ = [
+    "assign_connection_geometry",
+    "copy_boundary",
+    "edit_attributes",
+    "remove_boundary",
+]