* Add support for cached_properties to slotted attrs classes.
* Remove locking from implementation
* Add test for multiple cached properties and fix bug
* Add changelog file
* Document slotted cached properties
* Add cached_property hypothesis check.
* Only run cached_property imports on python 3.8+
* Use cached _obj_setattr instead of `object.__setattr__`
* Correctly resolve mro for __getattr__ in cached properties
* Use _get_annotations rather than branching on class dict entry
* Optimise __getattr__ code by front loading branching, and injecting locasl variables
* Remove unnecessary `__attrs_original_getattr__` from class dictionary.
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Co-authored-by: Hynek Schlawack <hs@ox.cx>
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