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/style/__init__.py

@@ -38,3 +38,18 @@ from .unassign_material_style import unassign_material_style
 from .unassign_representation_styles import unassign_representation_styles
 
 wrap_usecases(__path__, __name__)
+
+__all__ = [
+    "add_style",
+    "add_surface_style",
+    "add_surface_textures",
+    "assign_material_style",
+    "assign_representation_styles",
+    "edit_presentation_style",
+    "edit_surface_style",
+    "remove_style",
+    "remove_styled_representation",
+    "remove_surface_style",
+    "unassign_material_style",
+    "unassign_representation_styles",
+]