IfcParseWrapper: use swig feature to override base classes

Needed to make all attributes be resolvable statically.

src/ifcopenshell-python/ifcopenshell/ifcopenshell_wrapper.pyi

@@ -21,6 +21,8 @@ from typing import Any, Literal, Union
 from typing_extensions import Self
 
 import ifcopenshell
+from ifcopenshell.entity_instance import entity_instance_mixin
+from ifcopenshell.file import file_mixin
 
 # `std::vector<xxx>` usually translated to `tuple[xxx, ...]`.
 
@@ -873,7 +875,7 @@ class entity(declaration):
     def subtypes(self) -> tuple[entity, ...]: ...
     def supertype(self) -> Union[entity, None]: ...
 
-class entity_instance:
+class entity_instance(entity_instance_mixin):
     def __init__(self, *args, **kwargs): ...
     file: ifcopenshell.file
     """Reference to IFC file to prevent it's garbage collection, if entity is still used."""
@@ -966,7 +968,7 @@ class face:
     def matrix(self): ...
     def print_impl(self, o, indent): ...
 
-class file:
+class file(file_mixin):
     def FreshId(self): ...
     def __init__(self, *args): ...
     def add(self, entity: entity_instance, id: int = -1) -> entity_instance: ...

src/ifcwrap/IfcParseWrapper.i

@@ -991,44 +991,22 @@ static bool express_Base_equals(const express::Base* self, const express::Base*
 %include "../ifcparse/spf_header.h"
 
 %pythoncode %{
-### hack hack hack
-### we trick swig into inheriting from our own extension class
-### that way we do not constantly need to decorate/undecorate
-# @todo is there no official way to do this?
-_old_object = object
-from .file import file_mixin as custom_base
-object = custom_base
+from .file import file_mixin as _file_mixin_base
 %}
+%feature("python:abc", "_file_mixin_base") ifcopenshell::file;
 
 %include "../ifcparse/file.h"
 %template(instance_streamer) ifcopenshell::instance_streamer<ifcopenshell::file_reader<ifcopenshell::full_buffer_impl>>;
 
-%pythoncode %{
-### hack hack hack
-### restore
-object = _old_object
-%}
-
 %include "../ifcparse/file_open_status.h"
 
 %pythoncode %{
-### hack hack hack
-### we trick swig into inheriting from our own extension class
-### that way we do not constantly need to decorate/undecorate
-# @todo is there no official way to do this?
-_old_object = object
-from .entity_instance import entity_instance_mixin as custom_base
-object = custom_base
+from .entity_instance import entity_instance_mixin as _entity_instance_mixin_base
 %}
+%feature("python:abc", "_entity_instance_mixin_base") express::Base;
 
 %include "../ifcparse/express.h"
 
-%pythoncode %{
-### hack hack hack
-### restore
-object = _old_object
-%}
-
 %include "../ifcparse/schema.h"
 %include "../serializers/RocksDbSerializer.h"
 %include "../ifcparse/logger.h"