It seems that Python 3.11 requires the custom data type Nullable to
implement the __hash__() function, otherwise initializing dataclass
annotated objects fail with the following stack trace:

```
  File "/home/sag/projects/project-chip/connectedhomeip-v1.1/.environment/pigweed-venv/lib/python3.11/site-packages/chip/clusters/Objects.py", line 385, in Commands
    @DataClass
     ^^^^^^^^^
  File "/usr/lib/python3.11/dataclasses.py", line 1223, in dataclass
    return wrap(cls)
           ^^^^^^^^^
  File "/usr/lib/python3.11/dataclasses.py", line 1213, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/dataclasses.py", line 958, in _process_class
    cls_fields.append(_get_field(cls, name, type, kw_only))
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/dataclasses.py", line 815, in _get_field
    raise ValueError(f'mutable default {type(f.default)} for field '
ValueError: mutable default <class 'chip.clusters.Types.Nullable'> for field capacity is not allowed: use default_factory
```

Since all instances of Nullable are the same "value", we can return a
static 0 as hash value.