Dan Albert 2f2ebff674 Fix merged classvars in UnitType descendants.
```
>>> class Foo:
...     bar = 0
...     @classmethod
...     def set_bar(cls, v):
...             cls.bar = v
...
>>> class Bar(Foo):
...     ...
...
>>> Bar.set_bar(1)
>>> Bar.bar
1
>>> Foo.bar
0
>>> class Foo:
...     bar = {}
...     @classmethod
...     def add(cls, k, v):
...             cls.bar[k] = v
...
>>> class Bar(Foo):
...     pass
...
>>> Bar.add(0, 1)
>>> Bar.bar
{0: 1}
>>> Foo.bar
{0: 1}
```

The collections are copied by reference into the descendants, whereas
_loaded is copied by value, so that one can stay. Before this patch,
every subtype was loading because _loaded was set per subclass, but they
were all registering with a common collection defined by UnitType rather
than their own class.
2023-04-26 23:09:57 -07:00
..
2022-09-27 18:24:49 -07:00