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/pset_template/__init__.py

@@ -33,3 +33,12 @@ from .remove_prop_template import remove_prop_template
 from .remove_pset_template import remove_pset_template
 
 wrap_usecases(__path__, __name__)
+
+__all__ = [
+    "add_prop_template",
+    "add_pset_template",
+    "edit_prop_template",
+    "edit_pset_template",
+    "remove_prop_template",
+    "remove_pset_template",
+]