1) It wasn't removing ownerhistory in the case if task was RelatingObject in IfcRelNests
2) Replaced handling of IfcRelNests as an inverse with direct api calls.
3) Added some basic tests.
In IFC4X3 IfcQuantityCount is now more strict and requires only interger values.
Error for a reference:
TypeError: attribute 'CountValue' for entity 'IFC4X3.IfcQuantityCount' is expecting value of type 'INT', got 'float'.
order of objects in .RelatedObjects is important (e.g. for cost items, it's the order of their appearance), so we should maintain it and cannot use sets for .RelatedObjects
E.g. previously set_element_value with query "material.item.Material.Name" would fail with error "Material property is expecting an IFC entity and not a string".
But now it will detect that "Material" property is not a last key in the query and will pass `.Material` value forward and try to set it's `.Name` attribute with value.
The main goal is to make sure get_element_value and set_element_value would have a same result for same queries.
removed part of test_append_two_type_products_sharing_the_same_material_indirectly_via_a_material_set for ifc2x3 compatibility and removed part is already tested in test_append_two_type_products_sharing_the_same_material_with_properties
When some test was creating an element and then removing it, it would also remove user and application as they wasn't used anywhere else.
`ifcopenshell.util.element.remove_deep2(file, history)` we use in every api for element deletion can possibly remove user and application which can be unsafe if `get_user` is returning some specific entity that then will become invalid.
Also fixed tests breaking due ifcownerhistory and user/application appearing in ifc2x3.
it was creating new applications and users every time `ifcopenshell.api.owner.settings.get_user` or `ifcopenshell.api.owner.settings.get_application` was called
ifcpatch ConvertLengthUnit - change used units from plural to singular names, to make it consistent across the api
more test coverage - test converting to more units and back from them
Andrej730